The hard drive is basically dying a quick death. Not surprising since the model is at least 10 years old.
The best advice I can give is to buy a new hard drive. A 1TB HDD is pretty dirt cheap online and has much greater capacity than your current HDD which is probably 160GB or so. Stop using the HDD immediately because further use will only degrade the HDD which can prevent you from copying over any important information to the new HDD.