If it's powered by the mains - i would check the fuse. If it's powered by USB i would try a different lead and/or slot.
If the above doesn't work i would take it apart and look for obvious faults/loose connections
Failing that, i would remove the drive and hook it up to the desktop and check that the drive is ok and to back up data.
If the drive proves to be ok and but you can't fix the caddy - buy a new caddy.