Have you tried the fdisk mbr command? If that doesn't see results you would have to perform a repair install for the XP installation. That will get repair and replace the main system files without wiping out the current installations of softwares and the folders. You will need the XP cd for this one detailed in the article seen at
http://www.michaelstevenstech.com/XPrepairinstall.htm
Ready for Knoppix Live for cd? With a live distro like Knoppix you can copy files from one hard drive to another when one becomes inaccessible. For the general description on the live Linux distro,
http://www.knopper.net/knoppix/index-en.html
The long list of download sites is found at
http://www.knopper.net/knoppix-mirrors/index-en.html