open a command prompt with admin rights, and type chkdsk c: /r
this will check the disk using windows utilities. Next I'd find out who the manufacture of the drive is and grab a copy of their diagnostic utilities and run those.
Finally I would run a defrag.
After looking at disk related things, I'd take a look in the window system log and see if you find any other errors that might be of use in fixing the problem.
FYI, even thought Spinrite is kind of pricey it's well worth the $80 (I don't work for them). A single copy is good for all of the HDDs you personally own, or if this is for a business, if you purchase 4 copies you can use it for the entire company...of course start with one copy to see if it makes any difference. They also offer a 100% refund if you're not happy with it.
