Sounds like something is wrong with the hard drive then, sometimes this is something amazingly simple (drive has come unseated from its socket) but its more likely gone faulty, still a slight chance the cmos setup is not correct. Suggest you follow habdab's advice above.
In a time of universal deceit - telling the truth is a revolutionary act. George Orwell
When the debate is lost, slander becomes the tool of the loser. Socrates