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How to Build a Computer - The Complete Guide


How to Build a Computer: The Basics

Building a computer is kind of like playing Tetris. You have a bunch of oddly shaped pieces that you have to fit together only 1 way so you need to pick the right pieces or it won't go together. Other than that, the assembly is really quite simple and anyone can do it with hardly any tools. You need to have some dexterity and patience, yes, but it's not something that should scare you into running to the first computer store, opening up your wallet and begging the dude working on commission to take everything you have.

The most important step by far is creating a bill of materials... what parts you need to buy. In order to do that you need to do a bit of iteration. What parts do I want that will give me the performance I'm looking for? Are they compatible with each other? No? Ok which parts are compatible? Do they give me the performance I'm looking for? No? So on and so forth. Eventually you'll whittle down your list to something manageable and then you have to go through the exercise all over again but this time comparing (what you want & what works) with (what's in stock at the local parts stores) and perhaps again with (what's within my budget). It's a pain to do this and usually requires a couple of dedicated hours at a computer doing online research at multiple store websites. However once you're done with that, assuming you didn't make any mistakes, the rest of the process is quite literally a breeze, especially nowadays because parts are better engineered to be "tool-less", color-coded and easy to connect.

After having built a couple of computers it will become second nature to you and you can capitalize on your unique skill set by charging other people to make computers for them or simply by making your own far cheaper than what you'd buy at the store. Plus it truly is a custom rig, designed just for you, with nothing missing and nothing that you didn't need or want to pay for.

How to Build a Computer: The Parts

Now comes the fun part. You have to research every component you need to build this computer. You need to research what's compatible with what, whether it's good enough to meet your needs, whether it's cheap enough to meet your budget and whether it's available in your area for purchase. That's a lot of variables so expect to make a lot of compromises. The easiest way is just to wing it the first time around and get a rough list in 20 minutes or so. Then go back and check for compatibility. Highlight the offenders and then research those parts specifically to see if there's a substitute that does work with the rest of the parts. If not, you may have to change one of the mating components instead. An hour or 2 later, after this sweep you should have a list that works. Go through it one more time for compatibility really quickly to check yourself and then add up the total. Then check stock in your local computer shop(s). Tweak the parts as necessary to satisfy cost and availability, hopefully without messing up the delicate balance of compatibility you've just toiled over.

How to Build a Computer: Defining Your Needs

You can think of it as your needs driving the computer's bill of materials but really it tends to be the other way around. The hardware falls into various price brackets based on how badass it is. The level of ridiculousness in the performance of a given component could only be warranted by a certain type of user. For example, if you are going to buy a video card at all, there's no point in getting one for $100. Might as well get a good one for $300-400. At that point you've pretty much established yourself as a power user or a gamer. If you get a good video card you have to get a good CPU and motherboard, as well as sufficient RAM so that none of these things bottleneck your nice expensive video card. Again... gamer. Let's face it, if you're not playing games, you can get away with a barebones computer and be quite happy. I just built my friend a $300 computer and it streams HD video and plays DX9 video games just fine on maximum quality, along with doing everything else you could think of.

When it comes right down to it, the most expensive part of the computer goes hand in hand with the second and third most expensive parts of the computer. You wouldn't splurge on one and not the others. The only thing computational cycles are good for are math and transferring massive amounts of data quickly so unless you're doing CAD for an engineering firm or working on the next release of Avatar, chances are you surf the web, watch youtube, use Twitter and other day to day stuff that you could do just as easily on a cheap smartphone. Not trying to insult the few people out there who have niche uses for their rigs or anything. I'm just saying most people need a computer because their old one is messed up or old or it broke... OR they're a gamer and their current machine is no longer good enough OR they plan on mining bitcoin with it. I would fit yourself into one of these 3 categories. The difference in price is around $1500 :D By the way, if you are planning to mine with your computer, you'll want to look here first:


The Chassis, Case, Tower or Shell

Unless you're the the kind of person who likes leaving a bunch of loose components on the carpet waiting to short out, catch fire or get stepped on, you're going to need a case to hold it all together. This is truly the backbone of your system or, if you're the automotive type, the chassis. The case serves many purposes: It organizes your computer's internal organs, keeps them from shorting out on each other, protects them from external hazards, provides a common electrical "ground" for the whole system, provides all the buttons and front panel ports, enables easy access to all your removable media drives and creates a path for airflow to properly cool all the components. It looks cool too and you can pimp it out so your computer has a personality of its own... if you want to.

When you buy a case there are a few very important things to consider. How big does your computer need to be? The case size is often referred to as a "tower". There are mini towers, mid towers and full towers. The larger towers are needed to hold more internals like drives and cards and larger motherboards as well. They sometimes have mounting points for smaller motherboards too. You need to know in advance how much guts are going into your computer, determine the corresponding motherboard size you need and the number of drive bays you need and size your tower accordingly. If you're in doubt you can almost always get away with a mid tower. It's the safe bet 99% of the time. Since you are sizing the case or "tower" for your motherboard, among other things, look at whether the case supports the micro ATX (uATX), mini ATX and/or ATX form factor. From smallest to largest these are universal sizes for motherboards and determine the mounting points inside the case. You want your case to have mounting points for the size of motherboard you plan to get or you'll be S.O.L. when you build the thing. Simply put, if you want more cards and memory and decide to go with an ATX motherboard, get a case that supports the ATX form factor.

Make sure your case comes with a fan. If it doesn't, read the box for the fan size and buy one. The case provides the cooling and if you don't have at least 1 fan you'll get away with it for a while but in the long run you're asking for serious trouble and thermal overload problems.

The front panel of the case contains all your USB and sound connections so you'll want to make sure you're happy with that and that all the physical ports are supported by the motherboard connections. Check the motherboard features to see about that.

Try to get a "tool-less" case. They are becoming more common these days and replace nuts and bolts with cams and levers. Anything to lower the chances you'll break something or injure yourself, resulting in a lot of profanity is a good thing :)

How many CD/DVD/Blue-Ray or front panels (for high end sound cards for example) do you want? Make sure there are enough 5.25" drive pays for them. How many hard drives or floppy drives (don't laugh, I still use them) do you want? Make sure you have enough 3.5" drive bays for those.


- Go for "tool-less"

- Select your form factor (uATX, mini ATX, ATX)

- Select your tower size (mini tower, mid tower, full tower/server)

- Get a case with a fan

- Make sure you have enough 3.5" and 5.25" drive bays.

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- Get a front panel that is compatible with your motherboard

Must be compatible with: Motherboard, # of components

Price: $40 - $300+

Brands: CoolerMaster, Thermaltake, Antec, Corsair


The PSU or Power Supply

This is a small heavy metal box with many wires and connectors coming out of it. It converts your 120V household AC to the various DC supply currents your computer needs. The connectors are also unique to the things they plug into.

First off, everything in your computer draws power, measured in watts. If you can, get a rough idea how much wattage you'll need by looking at the specs on each part. Big power consumers are THE VIDEO CARD, the CPU and to a lesser extend, the motherboard. If you add 150 watts on top of that you should generally be fine. In most cases your average computer should be fine with 500 watts but do the math or suffer the consequences when something blows up, hopefully the power supply and not the video card.

Check the connectors on the power supply. They're all listed on the back of the box. You need a very specific set of connectors to power a motherboard and CPU. Sometimes it's a 20 pin for the mobo, sometimes it's a 24 pin. The CPU can be 4 or 8 pins. Each of your hard drives and optical drives will require a SATA power connector which looks like a thin black rectangular connector with a little L-shaped key in it. Make sure you have enough connectors for all the powered items in the computer. The graphics card almost always needs its own power. In the past it ran right off the slot but nowadays you need either a 6 pin (2x3) connector or 2 6's or a 6 and an 8. The graphics card will dictate that so check the PSU to see if it has the right connectors. You may need a large white molex connector or 2 for the case fan or an old drive you may try to scavenge from an older computer and floppy drives take small white 4-pin connectors.


- Check the wattage of the PSU vs the sum total of all the parts

- Check the connectors: 1 mobo, 1 CPU, 0/1/2 video card, various SATA, 1 molex, 0/1 floppy

Must be compatible with: Everything

Price: $30 - $150+

Brands: Cooler Master, Thermaltake, Antec, Corsair


The Mainboard or Motherboard

This is the most important part of the PC. It is the architecture for the entire computer and everything plugs into it. Generally speaking, the size (form factor) dictates how much stuff you can plug into it. If you want a power PC or gaming PC, get an ATX. If you're building something more of a budget computer, get a uATX. They are cheaper and smaller.

The most important parameter to look at when picking a motherboard is the SOCKET. Don't screw this up. I'll say it again. DON'T PICK THE WRONG SOCKET. The socket is the thing you plug the CPU into. It's a large array of holes and they must line up perfectly with the CPU. This is why you need to pick the motherboard at the same time as the CPU so shop for them simultaneously. Check the processor socket type and pick a matching motherboard. Make sure the motherboard can handle the power draw of the CPU as well. It should tell you what it's rated for.

Check the RAM slots. Check the speed and amount supported. Make sure your RAM is the right speed and that you can get enough GBs given the slots that are available.

Check the expansion slots including video slot. You will want to have a PCI Express or PCI-E slot that has a version high enough to support the video card you plan to buy. Make sure there is physically enough room for the card as many cards take up 2 slot positions and are sometimes very long and may hit other components on the mobo because the manufacturers aren't always clever enough to make room for the biggest cards. If you have old cards that take PCI slots, you'll have to find a mobo that has those slots.

Check the back panel. This is where all the ports are. Check to see if it has what you need. If you have old printers or serial devices you'll either need those ports or some sort of dongle that converts to them. Check that you have enough USB slots. Check whether you need a ps/2 style (round plug with pins) mouse and keyboard connector. Check if it has integrated LAN (these days it's impossible NOT to have this). Check if it has integrated video and sound. If there's a port, the video is either integrated on the motherboard itself or on the CPU so you don't need a video card. Same with the sound. If the holes are there, you don't need a card.


- Pick a motherboard form factor that suits your feature needs

- Check the socket of the motherboard and get that kind of CPU

- Check RAM slots to see if it supports enough RAM for you

- Check expansion slots to see if it supports the cards you want to install

- Check the back panel to see if it has the ports you need to plug in everything

Must be compatible with: Everything

Price: $50 - $250

Brands: ASUS, MSI, Gigabyte, Asrock, Biostar


The CPU or Central Processing Unit

This is the Administrator of your computer, the brains of the operation. Whereas graphics cards are good at doing lots of tedious and repetitive math, CPUs are good at doing ever changing complex tasks that they weren't specifically designed to do. Therefore it's very important to make sure you don't create a bottleneck for your PC by picking a weak CPU and pairing it with a strong video card or you'll be wasting money. CPUs are characterized by their speed (MHz, GHz), the number of cores they have (which dictates how many things they can do at the same time), the cache (which determines the speed of data retrieval for frequently accessed info), the power consumption (in watts), the fabrication process (measured in nm) which determines how many transistors can fit on the die and the socket, which is important when pairing a CPU with a motherboard. Basically you want high speed but low power consumption and cost. There's a trade-off too because you can only go so fast (~3 GHz) and then you need more cores to further increase computational power. Both speed and number of cores increase cost but you can look at different combos of the 2 and see if you can get a price break.

Then there are APUs. These are fairly recent developments in the world of computers and now there are more of them than CPUs. Basically it's a CPU with a GPU (graphics core) embedded in the die. The graphics cores used to be included on the motherboard but when you put them on the CPU it decreases latency and increases performance, not to mention it cuts down on packaging space and system complexity. For those of you buying graphics cards you won't care about APUs. You can use them or not and it won't matter much but if you don't want to invest in a video card, an APU is the way to go.

Make sure you buy a CPU with a heat sink. The CPU itself is a tiny chip while the heat sink is a massive thing with metal fins and a fan. You can't run a CPU without a fan but you can buy one that way, which makes it prone to error if you don't know any better. Try to fire up a PC with no CPU fan and it'll melt on you in minutes... or more than likely trip the BIOS to go into fail-safe mode so that doesn't happen. Don't let it get that far. Buy a CPU with the heat sink included. It may come with thermal paste applied already or in a separate reservoir. This you have to squeeze all over the CPU core before you place the heat sink on top. It's a liquid buffer that helps heat flow out of the chip more quickly. It's important so don't lose it or wipe it off.


- Buy a CPU that matches the socket of the motherboard you are using
- Buy an APU if you don't have a graphics card and the motherboard doesn't have integrated graphics
- Buy a CPU in the same performance bracket as your graphics card
- Buy a CPU with a heatsink and thermal paste included

Must be compatible with: Motherboard

Price: $50 - $400+

Brands: Intel, AMD

The RAM or Random Access Memory

RAM is really fast, temporary memory that is used for frequently access to fairly large volumes of information. It's very fluid and very fast. If not for RAM your computer would bog all the time as it would use the hard drive constantly to process information even if it just worked on that data a second ago. There's a direct correlation between RAM performance (and capacity) and your computer's speed. Large programs and games pre-load large amounts of data into RAM so that the CPU can work on it readily. As such you'll want to have some notion of the most labour intensive program or game you expect to run. Games are a good choice because they rely heavily on RAM. Pick a really feature packed, shiny game and check the memory requirements. Usually 4 GB is enough but someone who just uses Excel could easily live with 2 while someone else playing an MMORPG space empire game and running a Bitcoin mining operation in the background might like to have 6 or 8 GB laying around. Remember to check your motherboard to see how many slots there are for RAM. If you only have 1, you may have to put all your memory in 1 "DIMM", which is basically 1 chip you plug in instead of 2 with half the memory each. Fewer DIMMs jack up the price but are better for expandability of your rig.

Next check the speed of the RAM. It's measured in MHz like 1600 MHz as an example. The motherboard will clearly indicate the supported speeds so pick RAM at one of those speeds, the higher, the better but also the pricier. Don't mix 'n' match either. While you can mix capacities (1GB and 2GB DIMMs), you should never mix speeds (1333 MHz and 1600 MHz). It won't work and could be hazardous to the computer.


- Size your RAM capacity based on the software you plan to use

- Pick the highest speed you can afford, which is listed on your motherboard

- Never mix and match RAM speeds

Must be compatible with: Motherboard

Price: $15 - $200+ (and beyond, varies wildly on how much memory you want)

Brands: Corsair, Mushkin, Kingston, G.Skill, AMD, Pariot, ADATA

The HDD or Hard Drive

Hard drives come in 2 flavors now. The conventional type with a spinning platter and the solid state kind. Solid state has no moving parts and has faster access times but tends to be smaller in capacity and more expensive as it is a technology still in its infancy compared to the long track record and manufacturing infrastructure for conventional hard drives. Both are perfectly good choices and it really depends on whether you want the ultimate in speed or better value per GB. The hard drive is where all your programs and data are stored semi-permanently. That is, if the power goes out your hard drive retains data but the RAM is erased. Unlike RAM however, hard drives are pretty slow and the data is meant to be cached somewhere before being used. The capacity you choose depends on what sort of stuff you plan to store on your machine. If you like to put movies, games and music on your machine, you'll need a big hard drive. If you're mostly doing work on the computer, you'll need far less. Hard drives interface with the motherboard via a serial ATA connection or SATA. Aside from the power connector going to it you'll need a SATA data cable which is a thin red cable with small thin L-shaped black ends. Earlier hard drives used parallel ATA, which looked like a broad flat ribbon cable with several strands in it and a gray rectangular connector on the end. These hardly exist today so don't worry about them. The SATA standard is all you need to know now. You'll get a cable or 2 for free included with your motherboard.

Hard drives (the spinning kind anyway) spin at a variety of speeds but most of them spin at 7200 RPM. Don't get anything slower than that. The slower ones suck. You can gang several hard drives together in what's known as a RAID configuration in order to either protect your data by duplicating it on different physical disks or to speed up data transfer by storing alternate bits on different disks and accessing both simultaneously, exploiting 2 buses at the same time. Whether you do this depends on your needs and most users don't need to because it's unnecessary for the average consumer to have that level of speed or protection. Server administrators might want to do it though.


- Decide on either conventional or solid state hard drives

- Make sure you have a SATA cable for each physical drive you buy

- Determine how much capacity you need based on what you store on your PC

- RAID configurations give you extra speed or security

Must be compatible with: Motherboard, Case, PSU

Price: $50 - $600+

Brands: Western Digital, Seagate, HP, Mushkin, Intel, Kingston

The GPU or Video Card

Ahhh here we go :) This is what you've all been waiting for gamers! The video card drives all your video gaming and movie loving fantasies. It accelerates 3D graphics and renders crystal clear movies at blazing speeds while the rest of the computer put puts along. The video card, usually a massive dual-slot, heavy S.O.B. uses the fastest bus lane in the motherboard, the mighty PCI Express 16x lane. If that's not good enough for you, some motherboard have 2 of them so you can run a pair of cards side by side.

Video cards almost always require their own power and the PSU should have special PCI-E connectors just for the video card. Any good PSU will have a pair of 6 pin cables and the option to use a 6 and 8 pin configuration. If it's "Crossfire" or "SLI" ready, you will have even more of them so you can use multiple cards.

Not all PCI-E slots are the same. There are different version numbers and sometimes they are not backwards compatible. You have to makes sure that the card you're buying will work with the slot you have. The card and motherboard will both tell you on the specs what versions they support so just match them up.

The video card has its own video RAM aside from the system RAM we spoke of earlier. Any graphically intensive application will specify BOTH types of RAM and what the minimums are. Make sure your video card is sized appropriately to handle the load imposed on it by whatever software you expect to use.

On the back of the video card you'll have your ports for connecting to a monitor. There are many types of ports including VGA, DVI, Display Port, S-Video, HDMI, etc. If you have an older monitor with only a VGA cable, you may have trouble connecting it to a newer card. You can still do it though if you buy a dongle that converts from, say, DVI to D-Sub (VGA). Newer monitors won't be a problem though as they likely use either DVI or Display Port.

Expect to drop several hundred dollars on a good video card if you want to do better than the integrated video on your board or APU (provided you have one). You can however look at PassMark benchmarks on the internet that will give you an idea of how various cards rank in terms of performance per dollar. This will help you get the best value.

As mentioned, video cards draw a ton of power. Check your PSU and make sure it has enough rated wattage to support the peak load of the video card + a buffer of about 150 watts for everything else. PSUs often don't just pump all their current to the first device that asks for it. Rather, they distribute current on different rails so even if the "total" rated power is 500 watts, you won't get all of it for 1 device. Be conservative and either size up the PSU by a healthy margin or size down your graphics card.

Lastly, check the physical dimensions of your card. It "should" fit but if it's particularly long or massive, it may crash with other components on the motherboard like heat-sinks or capacitors. If any metal on the card shorts to the motherboard you could blow the whole works so best to check the dimensions ahead of time!


- Determine the PCI-E slot version and whether it matches your card

- Determine the card's peak load and whether the PSU can handle it

- Select a card with enough video RAM for the programs you'll run

- Check the PSU's connectors to see if you have the right ones

- Check the back panel to see if your monitor will plug into the card

- Check the dimensions of the card vs the motherboard

Must be compatible with: Motherboard, PSU

Price: $50 - $1200+

Brands: (AMD, NVIDIA) provided by: ASUS, Sapphire, MSI, PNY, Gigabyte, HIS

The Sound Card

Sound cards are simple PCI-E 1x or PCI cards that handle all audio tasks that the CPU would otherwise take on. Aside from offloading some of the work, they also excel at improving sound quality through the use of very high quality electronic components and sophisticated software. You can remove artifacts, add sound effects and play with the tone of your audio to get the best experience possible. Gamers and musicians particularly enjoy having a sound card because of the improved fidelity it offers. It also provides a means of connecting multiple speakers, headphones, microphones and digital I/O. They are typically low power devices and run right off the bus. They are smaller too and shouldn't pose much of a hassle to pick or install. You're more likely to have a problem with the provider's driver support than anything else.


- Buy a sound card if you have a slot to spare and are really into high quality audio or games.

Must be compatible with: Motherboard

Price: $50 - $250

Brands: Creative, ASUS

The DVD, Blue Ray or Other Optical Drive

These are fairly generic, run of the mill components which don't cost much and perform as advertised. You'll need at least 1 to install software and play movies so grab a DVD writer for 20 bucks. You just need an additional SATA power and SATA data cable, like the ones your hard drive used. You also need space in your case... a 5.25" drive bay to be exact. It's sometimes worth it to have 2 drives if you ever find yourself loading a lot of different types of software and don't want to wait for 1 to finish or if you wan to burn multiple disks to save some time. I have 2. Normally I'd say it's overkill but at 16 bucks each, you can't go wrong.


- Buy one

- You need an extra SATA data and SATA power cable

- Your case needs at least 1 5.25" drive bay

Must be compatible with: Motherboard, Case, PSU

Price: $15 - $100 (Don't spend more than $30)

Brands: LG, Samsung, LiteOn, Pioneer, ASUS

The Rest: Keyboards, Mice and Monitors

The only thing you need to concern yourself with as far as the computer is concerned is whether the correct ports exist to plug in these peripheral devices. Keyboards and mice are either USB these days or PS/2 if they are older. We all know what USB looks like and PS/2 is a round connector with several pins inside, usually color-coded on the back panel by green and purple.

The monitor will have either a D-Sub type VGA connector which is small and trapezoidal in shape, a DVI connector which is rectangular with an asymmetrical pin arrangement inside, or Display Port, which kind of looks like a bigger USB plug. It could also be HDMI, which looks quite similar to a Display Port.

Monitors use their own power supply and you should plug them into the same power strip that the computer is using to prevent ground loop issues from bad house wiring. Keyboards and mice are very low power and use bus power from the motherboard directly.


- Plug your monitor into the same powerstrip as the computer

- Check the monitor plug vs the ports on the back of your PC

- Check the mouse and keyboard connectors vs the back of your PC

Must be compatible with: Motherboard

Price: $5 - $200

Brands: Logitech, Microsoft, Others

How to Build a Computer: The Assembly Process

The number 1 rule in building anything made of electronic circuits is to bloody ground yourself! A grounding strap that goes around your wrist and clips to a metal work surface is cheap insurance against frying your new parts because you sat down in your sweatpants on your velour couch on your shag carpet floor. If you're going to be an idiot, at LEAST put the computer case on the floor next to you as you work and touch it with one hand while handling parts with the other.

The second piece of advice is to start by making a sub-assembly of the motherboard, CPU and RAM. This is easy and can be done very comfortably on a table. You can then put the whole thing in the case rather than trying to install millions of tiny cpu pins inside a recessed, dark chasm because you installed the motherboard first.

The third piece of advice is to have all the right tools and bags of parts organized before you start. Get a small Phillips screwdriver, needle nose pliers and a little flashlight. Then collect all the little bags of screws and stand-offs that came with your case and figure out what they're for. Arrange them on your work space so you have easy access to them.

With that said, let's go step by step:

Lining Up the CPU With the Socket


1) Unpack the motherboard and lay it front and center on your work space. Find the large square socket for the CPU and lift up on the thin metal lever you'll find on one side. It should lift up to 90 degrees and cause the socket holes to open up.

2) Unpack your CPU and remove only the chip at this time.

3) Find the small golden triangle on the CPU chip and align it with the motherboard socket so the corner of the chip with the triangle lines up with the socket's triangle.

4) Drop the chip into the socket. This step requires NO FORCE AT ALL. NONE WHATSOEVER. If the chip does not immediately and fully fall flush into the socket, it's not lined up. Lift it off, check things out (maybe the pins are bent?) and try again. Remember, DO NOT PUSH.

5) With the CPU flush, push the lever on the socket back down and lock it. You'll hear a faint crunching sound. This is normal.

6) Remove the heat sink and thermal paste (where applicable) from the CPU box. Apply the thermal paste to the top of the CPU chip.

7) The heat sink has a spring-like bracket on it that will grab onto 2 hooks on either side of the socket. Lower the heat sink onto the top of the CPU chip so that the ends of the bracket line up with the retention hooks on the socket itself. Fit the heat sink bracket ends around the hooks and then rotate the nearby plastic cam handle on the heat sink, which will tighten and lock the bracket into place so the heat sink can't move.

8) Using your motherboard documentation, find the CPU fan pin and plug the heat sink's fan cable into the motherboard.

9) Unpack the RAM DIMMs and plug them one at a time into the RAM slots, which are very long and located right next to the CPU. Now, unlike the CPU, the RAM modules will require A LOT of force so be generous and push them down until the retention tabs on the ends click into place. Just make sure you don't push the DIMMs in backwards. They only go in one way.

10) Motherboard sub-assembly is complete.

Securing the Cam Handle On a Heatsink


11) Put the motherboard aside and unpack your case. Remove any fasteners, bags, etc. and open the side panel. Lay the case on its side and unpack your PSU.

12) There are grooves in the sheet metal inside your case that serve as a tray of sorts that you must use to install your PSU. You'll know you found the tray because it's the highest thing on the back of the case and there's a big opening in the case for the back of the PSU to be accessible. The PSU should have a vent with a fan and a power switch on it. Make sure to have that pointing out the back of the case and slide it in the tray. Use the correct fasteners to screw the PSU into place, with all the cables hanging on the inside. Try to keep all cables as organized as you can since the next part is tricky.