Open the external case, . :D
Try to find the exact model of harddrive, replace the logical board from the other one and set it on the dysfunctional one. Now, try to access the data, that should revive the hard drive.
if not , shake your harddrive and make sure it gives out some sort of noise, put your drive in the freezer for two hours, get it back , let it thaw and connect it. Try to back up as fast as possible, the moment it starts to get heated up, it won't function. Just be very fast. I know that damn rattling sound.
and don't try to open up your drive's internal, the moment you open it up, and the light hits the plates, your drive is permanently baked.
goodluck.
