Initial Problem:
Every time you download or install a new game, application, or software update, you make changes to your computer. Sometimes that change may make your system unstable. Have you ever wanted to go back to the way it was? With System Restore, you can.
System Restore works a lot like the Undo command in Microsoft Word. You can use System Restore to remove any system changes that were made since the last time you remember your computer working correctly. System Restore does not affect your personal data files (such as Microsoft Word documents, browsing history, drawings, favorites, or e-mail) so you won't lose changes made to these files.
To restore Windows Vista click here
Solution:
If Windows XP will start:
- Log on to Windows as an Administrator.
- Click Start, point to All Programs - Accessories - System Tools - System Restore.
- On the Welcome to System Restore page, click Restore my computer to an earlier time, and click Next.
- Or type or paste the following command in the Start - Run box then press Enter.
%systemroot%\system32\restore\rstrui.exe
This command can be used at the Safe Mode Command Prompt also.

On the Select a Restore Point page, click on a bold date on the calendar pryer to the day of the problem stated. There may also be a restore point for an earlier time on the same day. Try to use a restore point as close as possible to a time just before the problem started. If the problem persists, an earlier restore point can be used.

On the Confirm Restore Point Selection page, click Next. System Restore restores the previous Windows XP configuration, and then restarts the computer.

If Windows will not start in normal mode
System Restore can be run form Safe Mode or Safe Mode Command Prompt.
Warning: When restoring a system from Safe Mode or from the Command Prompt an Undo restore point will NOT be created!