I suggest a full hard disk scan - you can get disk utils from Western Digital and Seagate (including Maxtor) for their drives. Presumably also for IBM and others.
Put it through a complete deep scan, let it attempt to map out any bad sectors.
If time is money, though, buy a replacement HD - or even a new PC!
SD
PS - If it is a faulty disk, it may still be under warranty. I've just had a Seagate disk replaced free (OK, £3 postage), although it's a factory refurbished replacement, so worth checking.