Hard drives are very cheaply made these days, and a good chunk of them will fail. Defragmenting won't stop hardware faults, and the clicking is an indication of a fault.


Copy everything off the clicking drive, and then dispose of it. Don't wait for it to fail entirely. If it's under warranty (Seagate is typically 5 years, everyone else 1 year), see if you can get an RMA # to ship it off for a replacement.


edit, re Windows purchase: I think if you install on a fresh drive, and not over top of Vista, it will ask you to enter your Vista key during installation. I don't think you need to buy another copy.