I have a non-working 17" imac hard drive in my hands, hooked up to a firewire external enclosure, for troubleshooting. The hard drive will spin up, but the needle arm moves back and forth, over and over again. I opened it up obviously, to find that out. There seems to be no scratches on the drive, and it spins up just fine, just the NEEDLE ARM moves back and forth, and makes that 'startup click' sound over and over, like its trying to do something, but failing.

Is there anything I can try? even if I'll screw it up and ruin the drive, its worth it.