Sounds like a corrupted file system. You can use a Windows 7 disc to get to the Recovery Console and run chkdsk.
You can download a X86 (32bit) or X64 (64 bit) from here: Download Windows 7 ISO (Official 32-bit and 64-bit Direct Download Links)
Burn it to a DVD using ImgBurn
at 4X speed (or the slowest you can get). Boot the DVD, take the Repair Path: How to Boot to the System Recovery Options in Windows 7
From the Command Prompt, enter chkdsk /f
and press Enter. Let that complete, remove the DVD and reboot, see if that fixed the problem.