Here it is. The final step of our How to Build a PC guide. You've got your brand-new PC ready and waiting. All we need now is to give it an operating system. I'll be taking you through how to install Windows 10 in this particular article (it really isn't as bad as everyone says it is, even if it can be immensely irritating sometimes), but most of these steps should also apply to older versions of Windows as well if you'd rather stick with something like Windows 7.
Step 1: With installation CD and DVDs more or less null and void these days, the easiest way to install a new operating system on your PC is to create a bootable USB drive. You can get one of these for Windows 10 direct from Microsoft if you can find one that's actually in stock - if so, skip to Step 3 - but otherwise the best thing to do is buy a digital key for Windows 10 and put Windows 10 on a USB drive yourself.
Step 2: Once you've bought your digital key for Windows 10, it's USB stick creation time. You can do this by using Microsoft's Download Windows 10 tool. Alternatively, if you're going down the Windows 7 route, then buy a Windows 7 licence key and follow these steps instead.
You'll need a fairly large USB stick - Microsoft recommends using a blank one with at least 8GB of storage on it for Windows 10 - but they don't cost much if you don't have one that's big enough. This 16GB SanDisk USB3 stick, for instance, costs just £6 in the UK or $8 in the US.
Stick the USB drive in a different PC to one you've just built (a laptop, for instance), download the media creation tool and then run it. Accept the licence terms, wait a bit for to sort itself out, and then when you get to the "What do you want to do?" page, click Create installation media for another PC, then click Next.
Select your language of choice, then the edition of Windows (the only option you have is Windows 10, so don't worry about this step) and then select 64-bit when it asks you what architecture you have.
Next, pick USB flash drive as your choice of media, select Next, and then double click on the USB stick in question from the list of available media.
It will then start downloading Windows 10 onto your USB stick, so you may have a wait a while for it to do its thing. Once it's finished creating your media stick, you're done!
Step 3: Remove the USB stick from your laptop and stick it in one of the rear USB ports on your newly-built PC. It won't recognise your front USB ports as bootable devices (trust me, I've tried), so put it in the back to save yourself another potential reboot.
Right, now it's the moment of truth. Time to turn on your PC! So go ahead and press that power button, and hopefully your PC has just turned itself on successfully. Now it's time to hammer some keys so you can enter your PC's BIOS settings - normally it's F2 or Del, but mash them both just in case.
You should now be in your PC's BIOS settings. The layout of this will vary from motherboard to motherboard, but the main thing you're looking is for the Boot Menu. Once you've found it, go to the Boot Configuration menu and make sure the USB stick with Windows 10 on it is at the top of the Boot Order.
Once the USB stick is set to the primary boot device, click Save and Exit in your BIOS and wait for your PC to restart. If you're worried about accidentally altering any other settings, your BIOS will tell you what changes you're about to make whenever you click Save and Exit, so you can check you've just changed the boot order and nothing else.
Step 4: When your PC restarts, it should actually come up with an Install Windows 10 page. Don't worry if the resolution's a bit wonky - this is just because your display drivers haven't been installed or updated yet.
Follow the instructions, selecting your language, time and keyboard preferences, and then click Next. Then select Install Now. Wait a few seconds and you'll then arrive at the Activate Windows screen. Enter your product key here and click Next. If you bought one digitally, you can probably find it in your email receipt.
Step 5: When you get to 'Which type of installation do you want?' select Custom: Install Windows only since this is a new PC. On the next screen, select the SSD or HDD you want to install Windows on.
You'll need to format it first since it's fresh out of the box, but once you've done that, it should say the drive now has unallocated space. Click New in the options below, and it should spit out a number of MB equivalent to the amount of storage on your drive. Hit Apply.
Windows will probably create a number of new recovery partitions on your chosen SSD - these are for in case things go wrong - but these are usually pretty tiny. Select the one labelled Primary (the biggest one) and hit Next.
Windows 10 will now start installing, and your PC will probably restart a couple of times in the process. So sit back, have a nice cuppa and wait for it to do its thing. Then, once it's done, it should plonk you on a Windows 10 set-up screen, just like if you'd bought a new PC yourself.
Choose your language, keyboard preferences and connect yourself to the internet, create a user profile, add a few security questions, decide whether or not you want Microsoft's digital personal assistant Cortana bugging you every five minutes, sort out how much data you'd like Microsoft to monitor, wait a bit for Windows to finish up installing and you're good to go.
Congratulations! Your brand-new PC is now ready to use. Pat yourself on the back, have a fifth cup of tea, and enjoy your shiny, fully self-constructed gaming PC. Told you it was satisfying, didn't I?
How to build a PC guide
How to install a power supply
How to install a motherboard
How to install a case fan
How to install a CPU
How to install RAM
How to install a graphics card
How to install an SSD / HDD
How to connect your system panel connector and case cables
How to put your case back together again and connect your peripherals
How to install Windows 10 - YOU'RE DONE!