If it's a 2.5" drive it might be getting insufficient power. I've had bad luck with premade external drives sucking...if it's out of warranty you could maybe open it up and see if the drive works on its own, and if so get a better enclosure or use a HDD dock.
Per the first post, he already took it apart and tried connecting it directly to his motherboard.
As far as 2.5" external enclosures and power goes, if it is USB you really should use a Y cable that powers the drive from two ports. Alternatively, if the enclosure has a jack for external power but did not come with its own power brick, the power brick from a powered USB hub will usually work provided the plug is the right size.
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