BTW - The absolute *best* tool I've seen, when even CHKDSK gives up, is "SpinRite" (grc.com).
It can take a while, but it's recovered data and drives for me that all else failed. If you think it's a hard drive problem. As someone mentioned, you can often hear it. It'll either whine, or sometimes you'll hear a rythmic pattern as it reads/times out/reads/times out/...
FYI - Mark