There are many reasons why you might want to reinstall Windows. Your PC could be infected with a virus, or it could be clogged up to the point where it is running slow all the time. As long as there's no problem with your hardware (which, in most cases, there won't be) then reinstalling Windows will give you back a working, speedy computer. 

In this guide we'll explain how to do that on Windows 10, Windows 8 and Windows 7.

Before you follow the instructions below, it may be worth giving your computer a spring clean. Clearing out clutter and stopping programs hogging all the CPU time and memory can help, but reinstalling Windows is a relatively fast way to blow out the cobwebs, including all the stuff that you just can't get rid of manually.

Warning: You will have to back up all your files, music, photos, videos and settings, and reinstall all your applications if you do a clean install. A clean install is where you completely wipe the hard drive and start from scratch.

It is also possible to reinstall Windows 'over the top' of the existing Windows. This is usually called an 'upgrade' and is a less drastic way to try to fix any problems preventing Windows from booting, and you shouldn't lose your files and apps. However, we'd still recommend backing up anything you can't afford to lose. 

The disadvantage of this method is that it may leave behind the detritus holding your PC back, and may not get rid of viruses. So in many cases, a clean install is the sensible option.

Note that if you have Windows 8, there are a couple of extra option: Refresh and Reset. For more, see our guide to reinstalling Windows 8.

How can I reinstall Windows 10?

Before you start: If you haven't done so already, you should link your Windows 10 product key with your Microsoft account. If you don't do this, you might not be able to re-activate Windows 10 after you reinstall it. Windows 10 doesn't necessarily have a product key and if you upgraded from Windows 7 or 8, you certainly won't have one.

So head to Settings > Update & Security > Activation. If the status says "Windows is activated with a digital licence" but says no more, then it isn't linked to your Microsoft account.

To fix that, go to Settings > Accounts > Your Info. Click "Sign in with a Microsoft account" and follow the prompts. Once done, you can check under Activation and you should now see that the message reads "Windows is activated with a digital licence associated with your Microsoft account".

Here are tips on fixing Windows 10 activation problems.

Reinstall Windows 10 on a working PC

If you can boot into Windows 10, open the new Settings app (the cog icon in the Start menu), then click on Update & Security. Click on Recovery, and then you can use the 'Reset this PC' option. This will give you the choice of whether to keep your files and programs or not.

There's also a link lower down which opens Windows Defender and lets you do a clean installation.

How to reinstall Windows

Reinstall Windows 10 on a non-working PC

If you can't get into Windows 10, follow the steps below.

First, turn on your computer and look for any messages which appear before the Windows logo. Some laptops and PCs come with a 'hidden' hard drive on which is a full backup of Windows. Typically there will be a message such as "Press F10 for restore options". Each PC is different, but you may find an option to reset the PC to factory settings. What this does is to delete everything on the hard drive and copy the hidden version of Windows back on to the hard drive so your computer will be exactly the same as the day it left the factory.

You can also try pressing the F8 key to access the advanced boot options menu, which should include a 'Repair Your Computer' option. 

If none of that works, try these steps:

1. Download Microsoft's Media Creation tool which will create a bootable USB flash drive with Windows 10 on it. You may need to use a working computer to do this if yours won't boot into Windows. Keep this drive safe for future reinstalls, too. You can also use the drive for upgrading an existing Windows installation simply by running Setup.exe from the drive when running Windows 7 or 8.

2. Boot the non-working PC from your USB flash drive. But before you do, ensure you've backed up everything, as the process will wipe your C: drive. If you haven't backed up any files, you may have to remove the hard drive and connect it to a working PC in order to copy them off.

3. If the PC won't boot from the USB drive, enter the BIOS by pressing Delete, F2 (or the key shown on the boot-up screen) and then look for 'boot' or 'startup' options where you can select a removable USB drive as the first boot device.

4. When the PC has successfully booted from your USB flash drive, you'll see a Windows logo and then a screen like the one below where you choose your language. Simply follow the instructions and but make sure you choose the correct hard drive and partition on which to install Windows. If it's a new drive, it will be blank, so you choose the only option available: the large unallocated space.

How to reinstall Windows 10

4. Once the installation starts, your PC will reboot. You'll see a Windows logo and a large circular progress indicator. Keep an eye on the install as it will reboot your computer several times and may ask you to remove the DVD or flash drive. 

How to reinstall Windows 10

How do I reinstall Windows 7?

This is how to reinstall Windows 7 from DVD. However, some PCs allow you to reinstall Windows from a separate recovery partition on your hard disk and, in that case, you should follow the manufacturer’s instructions. Alternatively, if you’ve lost your Windows 7 disc and your PC doesn’t have a recovery partition, take a look at our guide to reinstalling Windows without a disc.

If you're reinstalling Windows on the same hard drive as it's currently installed you have two choices: Upgrade or Clean install. The former will keep all your stuff but may not fix a problem you're having, while the latter will wipe your hard drive and you'll lose all the data from that partition (or the whole drive if there's only one partition on it). Make sure you've backed up everything you don't want to lose. 

Also, don't forget you’ll need to activate Windows after installation using the product key (the five groups of five characters shown next to 'CD Key:' in the image below) so make sure you can find it on a Microsoft sticker somewhere on your PC. If there’s no sticker or it’s illegible, you might be able to get it running Magical Jelly Bean Keyfinder on the PC in question. (When you install it, be careful not to also install the optional search bar.)

How to reinstall Windows 7 Step 2

With that done, shut down your PC put the Windows disc in the CD/DVD slot and start it up. All being well, it should boot from this. If it boots to Windows normally, you’ll have to use the BIOS menus to make your PC boot from a disk – see How to enter the BIOS for instructions.

How to reinstall Windows 7 Step 3

When you've made the computer boot from the DVD or USB drive, Windows Setup will start and on the first screen you need to specify your preferred language, time and currency format, and the nationality of your keyboard. Just follow the on-screen instructions.

How to reinstall Windows 7 Step 4

Next you’ll now be asked “Which type of installation do you want?” and both options will be explained. Choose the “Custom (advanced)” option will take you back to the way your PC was when it left the factory. (Note that you could try the Upgrade option to reinstall Windows "over the top" of your existing installation to see if it fixes a particular problem you're having. This will keep all your files, programs and settings intact.) We'll show you how to to a clean install here.

How to reinstall Windows 7 Step 5

Next you’ll be asked “Where do you want to install Windows?”. Sometimes just one partition will be shown, in which case just click on Next. If multiple partitions are displayed, select the first primary partition (usually the largest) before clicking on Next.

How to reinstall Windows 7 Step 6

Windows 7 will now be installed and progress will be reported in the list of actions and the progress bar. This could take some time. Often it’ll seem that the installation has got stuck in the “Completing installation” phase so be patient and don't turn off your computer.

How to reinstall Windows 7 Step 7

Finally you’ll be guided in setting up a user account. Also, you’ll need to provide the product key that you identified earlier. This will be used later when there's an internet connection to activate the new installation of Windows.

How to reinstall Windows 7 Step 8

Follow the instructions to select security options (we suggest accepting the default setting), the time and date format, and perhaps to connect to a wireless network and join a Homegroup if these are detected.

How to reinstall Windows 7 Step 9

Windows will now start but the desktop will look different and rather empty. Your next job, therefore, is to re-install the various applications that you use on a regular basis.

How to reinstall Windows 7 Step 10

Now go to Device Manager – search for it in the Start menu – and check that drivers have been installed for all the hardware. If you see and devices with an exclamation mark, go to the manufacturer’s website and download the latest versions. You should find the appropriate drivers by using your laptop’s exact model code; for a PC, you’ll need to know the motherboard make and model, and the model numbers of other key components such as the graphics card.

How to reinstall Windows 7 Step 11

Even if you see no problems, it's worth installing manufacturer-specific drivers (rather than the generic Microsoft drivers which Windows will have installed) for components such as the graphics card, motherboard chipset, laptop touchpad etc.

Plus, there may be manufacturer utilities (especially for laptops) which won't be reinstalled with a ‘clean’ copy of Windows. For example, some laptops have utilities which prevent the battery charging to 100 percent, prolonging its life.

Now, you can copy all your files back onto your PC that you backed up at the start. You’ll probably also want to select your favourite wallpaper and make all the other changes necessary to customise your PC the way you like it.

How to reinstall Windows 7 Step 12