Windows has slowed to a crawl. Applications won’t run. Your firewall won’t update or uninstall itself. System Restore hasn’t helped; neither have your assorted clean-up and antimalware programs. Only one option remains: reinstall Windows and start from scratch. But it’s a time-consuming job, and your PC could be unusable for a day or more. You could even lose all your data.

While we usually advise against reinstalling Windows unless you absolutely must (and certainly not because a tech support person thinks it could solve a complicated problem, such as getting you off the phone), sometimes it’s necessary.

Here’s our guide to making the process as safe and painless as possible.

Windows installation toolkit

Before you begin you’ll need a recovery tool. If you’re using the version of Windows that came preinstalled on your PC, that tool is probably in a hidden partition on the hard drive. That partition has the information necessary to restore the hard drive to its factory condition.

If your PC is a few years old, the recovery tool may instead be on one or more CDs or DVDs that were supplied in the box. The manual should say what kind of recovery tool came with the PC and how to access it.
If you’ve upgraded Windows since you bought the machine, the upgrade disc is now your recovery tool.

If you can’t find a recovery disc and the PC has no hidden partition, contact the manufacturer to see what it can do for you. Also see How to install Windows without the restore disc.

Following the installation, you’ll have to reinstall any programs you want to continue using. Collect the original discs or downloaded installation files, plus any associated licence keys. You’ll need an external hard drive with a capacity at least as large as your internal drive. Finally, you’ll need time – at least a full day, if not more.

Back up everything

How to reinstal Windows Things could go horribly wrong, so you need to make a backup of your hard drive and all the data stored on it. Use cloning software to turn the external drive into an exact copy of your internal hard drive. We recommend cloning the drive using EaseUs Todo Backup. Alternatively, you can create an image backup if you prefer.

A second backup of your data wouldn’t hurt. If you don’t have one already, create one using your regular backup program.
See our guide to the most suitable type of backup.

The Windows reinstall

The method for replacing a Windows installation depends on your recovery tool. If your PC came with a recovery partition, find the instructions for booting into the repair environment. Watch the screen as you turn on the PC; it might show a message such as ‘Press F10 for repair’. If it doesn’t, check the manual or search online for your PC.

If your recovery tool is a disc, boot up the PC from it and follow the prompts.

If your recovery tool is a Microsoft Windows disc, the tool will ask what kind of installation to perform. In Windows 7 or Vista, select the ‘Custom (advanced)’ option. In XP, at the ‘Welcome to Setup’ screen, press Enter to continue, rather than R for repair.

Once you have a fresh Windows installation, the hard work begins.

How to reinstal Windows Windows will need updating. The patching will happen automatically, but you can launch Windows Update and let it take care of things if you want to get it out of the way.

You’ll have to reinstall at least some of your drivers. You can use the discs that came with your PC, printer, scanner and so on, or you can download newer versions from the web. Alternatively, you can install the drivers from the clone you made.

If you reinstalled Windows from a disc that came from your PC maker and it’s one that returns your hard drive to its factory condition, you probably have a lot of junk programs that you’ll want to uninstall.

Windows’ own uninstaller often leaves remnants behind. Use Revo Uninstaller or Total Uninstall. Both utilities run the program’s own uninstaller, then clean up the remainder.

Revo Uninstaller is free, but Total Uninstall does a better job with uninstalls that require a reboot. Revo Uninstaller doesn’t work with 64bit programs; Total Uninstall does.