For this fix, it will require a full data wipe.
Be sure to back up all of your data that is important to you. Your going to need a few things to download first.
1.) USB thumb drive or blank DVD (Make sure your PC is bootable via USB or CD in BIOS.
Download this program and burn it to a disk. Do NOT unzip.
http://downloads.sourceforge.net/project/dban/dban/dban-2.2.6/dban-2.2.6_i586.iso?r=http%3A%2F%2Fwww.dban.org%2Fdownload&ts=1298878936&use_mirror=cdnetworks-us-2
Boot your computer with that disk, and follow the onscreen instructions to completely wipe your hard disk. Be sure you have the ability to re-install Windows.
If you have any further questions about the hard drive wipe, see here:
http://www.dban.org/faq