As Mart said, there's several S.M.A.R.T. testers available. As long as your HDD's are S.M.A.R.T. capable (which all are these days) and it's enabled in BIOS, any of those appz should help determine if your HDD is failing.
Even Speedfan (used to monitor pc temps & fan controls) has it built in.
Alternately, if you have a Seagate HDD then I'd download Seatools off their website. It can scan your Seagate or Maxtor drives (same company) for errors. Pretty sure other companies also have similiar software available for download.
It could be as simple as bad cables to your hard drives or time to reformat the drive & re-install windows.
But yet it could be a power issue as well. Power Supply isn't quite enough to run your system, rails going bad, etc.
The S.M.A.R.T. test coming back good is a shocker to be honest. I was fully expecting there to be errors on that disk as that explains everything in your original post.
Maybe it is just a hard to read master boot record, you can either fix it by formatting or trying to fix it. Tool to try and fix it are included in your windows install disk i think
