Hard drives are extremely fragile devices. I dropped my external 500GB hdd from about 20 cm height while it was turned on and it stopped working completely. The problem was that the motor could not spin the shaft. So I opened the drive, disassembled it and tried to rotate the shaft with pliers.
After some work I managed to fix it. Of course meanwhile I damaged everything else – heads, some scratches on the plates… Still I fixed the motor!
You can also see it in action: