First, try simply removing the drive from the bay (slide switch and pull out). Then, take a clean toothpick and gently rub across both sides of the tiny contacts inside the 50 pin connector on the unit's rear. You should see darkened points on the toothpick from removed oxidized film on the contacts.Then reinsert the drive back and check for function. Repeat several times the whole process if not resolved at fist.
You might get the drive running again this way.