I had this issue, couldn't get through a movie to save my life without it freezing up and coming back. Solution was to stop letting windows 7 put my hard drive to sleep. (not sleep mode, windows 7 cuts the drive after a while when it thinks you're idle or whatever - changing that setting, it fixed it)
In my case, both my OS and my stuff is in the same HDD. Come to think of it, I should separate them to ease the readership between the OS and the work files.