HFS+ or NTSF? Sorry to hear about a potential disk failure.
Are you certain it is not the connector (D.C. in?) ???
Is there an LED on the unit? Does it go off and on if you simply touch the connector. (some OWC models with fans have the transformer built in, AC in, not DC in).
If drive lunches on a Mac good news is sometimes possible to fix it with Diskwarrior 4.2/4.3 or at least get it running enough to clone it or if not, then archive and reinstall OS. But I'd change ownership on entire drive if that is the case and copy data over. You can smack the end of the drive while powered up held tightly out of the enclosure I.E. to restart the platter. (Two beat square wave buzz - which may be the heads vibrating) to get the platters spinning back up. We did this on tour in Atlanta with an EMAX II, HDD, of course we didn't carry 300 diskettes as a backup. Those were Quantum SCSI drives as in the early Macs and yes, even these you can smack the noncabled end to sometimes get the platter spinning (mind you this is a last ditch effort or you will have to send the drive to Marin County to Drive Savers).
I was able to smack a Caviar just recently and the platter spun up, the heads no longer vibrating, allowing it to attempt a book (and Diskwarrior)... but clone it immediately (SuperDuper)... and watch for 'slow down' error from Diskwarrior (if drive is malfunctioning).
WARNING -- some of my enclosures have D.C. inputs not AC. internal transformers and fans. Don't mess with open enclosures if AC power enters the external case unless you are an EE or trained electrician! 120-240 volts! OWC sells a D.C. powered 'Swiss Army' knife raw drive connector one could use to encourage the platter to spin up. Sometimes static causes it to freeze up... or heat messing with the bearings.