Q: Old hard drive in SATA enclosure not recognised?

Hello everyone,

I upgraded from my MacBook Pro 2011 and decided to try and use the old hard drive as an external drive. I bought a Dynamode 2.5" enclosure, plugged everything in and connected it to the new computer - only to find it's not recognised, doesn't even show. Whether it's on Finder or in the Disk Utility, it's as though nothing was connected - and yet the hard drive is making a whirring sound, generates heat, and the enclosure has a light on.

For more info, I've tried connecting it to a MacBook Pro bought a month ago as well as the MacMini I have in the office (both running Yosemite 10.10.x). Neither have shown any response. I haven't yet tried connecting it to any other OS. Any ideas what could be going wrong? Or is the enclosure defective and I need to get a new one?

Thanks!