Hi cranborile, from the info that you have posted it sounds like your the victum of a slowly dying hard drive despite the results of the hard drive diagnostic software. Usaully a reinstall of the OS would most certainly fix this issue....if I were you I would go ahead and buy myself a new hard drive or better yet if you an have an old drive lying around or you have friend that would lone you one that would allow you to diagnose your problem to see if the drive is truly gone bad.
Good Luck!