|That doesn't sound like any virus activity that I ever heard of, more likely faulty hardware is causing it.|
Test the hard drive with Seagate SeaTools for DOS which runs from a bootable CD: http://www.seagate.com/support/down...
You will need IMGBurn to make the CD from the SeaTools ISO file:
When you've made the CD, boot your faulty PC from it and SeaTools will eventually appear.
Select the system hard drive and run the extended/long test on it.
If it passes okay, test the RAM with Memtest86. Again, you need to make a CD from the downloaded ISO file & boot your PC from it: http://www.memtest.org/