Hard drives fail sometimes. It's something that will eventually happen to almost every drive.
Get a low-level scanning utility from the manufacturer's website, and do a full scan of the disk using a bootable floppy. That will tell you if there are errors on the disk surface itself. If you need information off of the disk and can't get it, there are recovery programs that will retrieve it even though the drive is dead. (R-Studio from R-Labs is the one I tried, but it costs money.)
I personally am going to think about moving to SCSI for single-disk systems. I'm running into lots of reliability problems with IDE drives.