Are you using the most recent version of Memtest? memtest+ 4.10
I was having a lot of random BSODs from a bad memory stick.
The bad memory (and probably crashes) corrupted a lot of Windows files which just compounded the problem. In the end, I re-installed Windows 7 to be certain.
Have you run CHKDSK? I've known CHKDSK to make things worse when it can't fix a problem, but I don't know an alternative:
How to Use Check Disk in Windows Vista — MAXIMUMpcguides – Windows Vista tips, tricks, help, and how-to guides
Or sfc.exe /scannow (System File Checker)
How To Use SFC /Scannow To Repair Corrupted Windows System Files - TECHRENA