|Is this a mains powered 3.5" external HDD or portable HDD?|
Is the drive spinning, trying to spin, making ticking noises etc.
Maybe more ideas to come from other helpers, but if all else fails, the tale below may help:
NOTE: LAST RESORT ONLY!!
Couple of years back, had a WD 3.5" external handed to me to try and fix.
It had taken a soft fall from desk to carpet, but the high torsional/gyroscopic effect of the spinning twin discs in the unit had somehow whacked the motor drive geometry out of kilter, causing it to stick. You could here it groaning etc at switch on, before it cut out.
At this time I hadn't a clue what was going on, but, nothing to lose, so unscrewed the top plate to gain access to the discs.
Being careful not to touch the discs or other vital bits, I noticed it struggling to spin up.
I found that just before the electronics cut the motor out, if I placed a long thin driver in a depression in the centre hub of the disc array and helped the motor along, it would slowly get up to full speed.
I was lucky in that it kept spinning for the next hour - long enough for me to retrieve a good chunk of the data on it.
Pure luck maybe, but I was pretty chuffed at what I managed to achieve.
Of course the HDD was scrapped after that. It wouldn't start up again during later attempts from a cold start. In any case, a drive opened up in such a way, not in a controlled, lab environment, would be a liability anyway, what with dust etc in the air....
So don't try to open up a good drive - only on a scrapper. ;o)