Not 1 but 2 problems

Help me out here please. I have one external WD hard drive that started disconnecting itself quite frequently. After taking it out of the enclousure it seemed to have some kind of wear and tear somehow. So when you plug it in you only have a brief window to transfer data (ranges from 4 to 14 gigs worth) before it disconects. I contacted WD and had a replacement drive sent. Now after a long and ardious task that is near completion the new drive is not being recgonized by the computer (and it seems the old drive has followed). Both are originally formatted for windows but I downloaded some plug in so that they would work for the mac. Maybe it needs to be updated??? I don’t know. But either way I am running out of time before I have to send one of the drives back but I can’t seem to get any data out from either of them. Help please. Thanks!

From what you said, I’m assuming you have a MAC computer, can you try to use those units on a windows computer, just to see what happens since they are originally formatted for windows