Did you actually reformat the hard drive or just do a restore/repair install? I suspect hardware failure. Can you run chqdsk? Does it show errors?
Right click on the C drive icon > properties > tools > error checking > checkmark both boxes.
You can also download memtest to check your ram.
http://www.microsoft.com/resources/d...us/chkdsk.mspx
http://www.memtest86.com/
http://www.ultimatebootcd.com/