Depending on the extent of the damage to the hard drive, you may have to rely on data recovery professionals (not best buy) to extract as much of the files as they can.
Probably the worst thing (other than totally corrupted data) is if the drive motor / read / write heads are total messed up. In that case it would be necessary to disassemble the hard drive to access the individual platter in a cleanroom (i.e. totally controlled environment), then mount it in a drive to access the data. Something like that is very expensive. Several hundreds of dollars and data retrieval is not guaranteed. Hopefully you do not need that type of help.