First see if the drive spins up with only power connected. If that works then try connecting the SATA data cable while the drive is still spinning. If the system doesn't recognize the drive after the data cable is connected then restart the system. If this doesn't help then the logic board or other components on the drive may be defective. If you have an identical drive you can try replacing the logic board. Other than that if the data is important I would recommend sending it to a professional data recovery outfit.
I used to recommend Actionfront, however they were acquired by Seagate and are now the official Seagate In-Lab Data Recovery
service. They have different services for consumer or business customers, with expedited (and more expensive) services available for the latter
. Let me know how things turn out, Scott.