Switch back to Windows XP

Currently have Windows Vista OS but trying to switching back to XP OS.

Whenever attempting to reformat, I see the error msg saying:

A prolem has been detacted and windows has been shut down to prevent damage
to your computer.

If this is the first time you've seen this stop error scree, restart your
computer. If this screen appears again, follow there steps:

Check for viruses on your computer. Remove any newly installed hard drives
or hard drive controllers. Check your hard drive to make sure it is properly
configured and terminated.
Run CHKDSK /F to check for hard drive corruption, and then restart your
computer.


I'm a rookie and don't know how to check drives. Definitely not virus
issues. Would appreciate giving me a a step-by-step solution. Thanks much..

CP