Googling around brings up links which indicate that your hard drive is probably failing. Test the hard drive with a diagnostic utility downloaded from the drive mftr.'s website or use Seagate's SeaTools For DOS. You will create a bootable CD with the file
you download. You will need third-party burning software to do this such as Roxio, Nero, or the free ImgBurn. Burn as an image, not as data.
Boot with the CD you made and do a thorough test of the drive. If it fails any physical tests, replace it.
If you can't do the testing yourself and/or are uncomfortable opening your computer, take the machine to a professional computer repair shop (not your local equivalent of BigComputerStore/GeekSquad).
MS-MVP - Elephant Boy Computers - Don't Panic!