OK, lets try different approaches.
1) It could be a boot sector virus. Try the kaspersky rescue cd. Download FREE Bootable Rescue CDs from Kaspersky, BitDefender, Avira, F-Secure and Others - Tweaking with Vishal
The only issue is whether the computer will be able to boot from the cd.
2) Possible RAM error. Try swapping out the RAM sticks- that is change their respective slots or take out all but one stick, then try reboot. 3) Possible bad hard drive. I dont know what brand hard drive you have but you can download the specific diagnostic and run it. HD Diagnostic
Edit: See if you can boot from a bootable usb stick (or a linux live cd). Heres how to make one (method 2): USB Windows 7 Installation Key Drive - Create
If you can, navigate to the folder c:\windows\minidump and copy any .dmp files in it, upload them here. http://www.sevenforums.com/tutorials...en-forums.html