Make sure you save (backup) things like Word documents, Emails, pictures, music files, favorites (internet bookmarks), etc to other medium such as CDs, DVDs, flash drives, etc BEFORE scrubbing your computer.
Make sure you have all the software CDs found ahead of time, including your operating system disc (Windows), Antivirus. Also have your drivers disks for your peripheral devices such as printers, scanners, digital cameras, etc.
Insert your Windows CD and restart your computer. When the computer restarts, a message should appear saying "Press any Key to boot from CD..."
Windows Setup will load the drivers it needs to install.
Choose the hard drive you want to install Windows to, and tell setup to format the drive in NTFS.
Follow the on-screen instructions to complete Windows setup.
Once Windows is reinstalled, first install your Antivirus and download all updates and patches. Then download Windows updates, then continue to install the rest of your software. Don't forget to copy the backed up data you did in Step 1.

Tips

If you're giving away your computer and want to permanently erase sensative data, use software such as "Autoclave Hard Drive Eraser" that erases everything without installing an operating system.

Warnings

Formatting a hard drive does not permanently delete the data on your drive! A professional can still extract data from a formatted hard drive.
Make sure any data you backup in Step 1 isn't infected with viruses

Article provided by wikiHow, a wiki how-to manual. Please edit this article and find author credits at the original wikiHow article on How to Reinstall Windows XP (start over with a slow or infected computer). All content on wikiHow can be shared under a Creative Commons license.

Wiping all files from a computer's memory would effectively render it useless, but it is possible to delete most or all nonessential files.

Wiping all files from a computer's memory would effectively render it useless, but it is possible to delete most or all nonessential files.