1. Insert a Windows XP Live CD into your computer and restart the PC.
2. Press any key when prompted to boot from CD into Windows XP.
3. Click 'Start,' 'Programs,' 'Accessories,' 'System Tools' and select 'System Restore.'
4. Click 'Restore my computer' and click on a restore point prior to the time your computer became unbootable.
5. Press 'Next' to restore the computer.