is this drive physically bad? as in is it clicking or making wierd noises? Does your comptuer recognize it in the BIOS at all? If its physically bad, you may be out of luck unless you have a clean room and spare parts but if you simply have bad sectors on the hard drive, you can try a few different things like formatting it or chkdsk to repair a current windows installation etc.
Only thing u can repair in a hard disk even if u have tools is the logic card,( the circuit board) provided the product is out of warranty. Also u can repair the connecting pins if u know how. Sometimes data center ppl can repair a hard disk to some extend with parts from a donor drive ( matching type of drive). Any repair or even damaged screw will void its warranty.