Have you run the HD maker's HD Diagnostic extended CD scan yet? What is the make of the HD? What does it report?

You'll need to determine the condition of the HD before proceeding, then if it checks out OK wipe the HD with the CD's Quick Wipe function.

If you don't know the maker of the HD use Seagate Seatools burning the ISO to disk with Windows Image Burner or ImgBurn