To save data on hard drive use either of the following:
• move HDD into another computer as an extra drive and copy important files.
• Boot to a Linux CD (do not install) and save files to removable media.
After saving your files, use XP disk to format drive and reinstall windows, then update windows, update drivers, then install programs, and change copies of your files back.
If you have any problem installing, check RAM with Memory test.
And test HDD with HD mfg.'s testing utility.