On 'the disk didn't fail' - I recently found Windows had 'deleted' the hal.dll file required for boot. I replace the hal.dll but it got removed again. It turned out to be that the disk was failing silently, without visible read errors in the logs - I replaced it with an SSD and it's been fine since. So in this case it was a disk failure, but on the surface it looked like a Windows failure.
If you are having unexplained file corruption, it could be a RAM error as well, of course.