You can use Window XP's System Restore to undo harmful changes to your computer and restore it's settings and performance. System Restore returns your computer to an earlier time, called restore point, without causing you to lose recent work, such as saved documents or e-mails. Changes made to your computer by System Restore are completely reversible. XP automatically creates restore points, called system checkpoints, and you can create your own restore points. This is useful if you are about to make a major change to your system, such as installing a new program or changing your registry.
Click on "Start" and select "All Programs." Open the "Accessories" and move to "System Tools," then click on System Restore. The next screen is a Welcome to System Restore.
Select "Restore my computer to an earlier time." The next screen displays a calendar showing choices of restore points. Select your desired restore point date and click "Next."
Click "Next" again to confirm your choice and the computer will start restoring itself. The system restarts during the restore process.