When i have a problem like this i take the drive to a friends house even though it is a different set up and see if it works in his. So try the drive in another pc if you can. If it does NOT work in another pc you can probably say it's dying or dead.
You might also check to see if DMA is on on your drive in your pc. Go to Device Manger and check the IDE channel the drive is on Properties then Advanced Settings.