I am going to go out on a limb and make some guesses about your hard drive:
A. It is an IBM
or
B. It is old
I have an IBM drive that started doing some funny things, like if it was an old drive, and it was actually not that old. IBM had a bunch of their hard drives made by Hitachi, and almost all of them came out faulty, and would get all messed up quite quickly. If you do have one of these hard drives, you can send it in, and have it repaired/replaced for free.
If your hard drive is not one of those IBM drives, then it is probably old and dying.
In either case, I would reccomend that you go get a new hard drive. I am preferential to Western Digital drives, but Maxtor is making some good drives now as well.
Buen suerte,
Smar969905
Young, foolish, and occasionally knowledgeable...