If you can get all the data from the drives, do so, then do a slow format of both and see if that resolves the problem. I am guessing you have tried the drives in different USB ports. It also could have something to do with the external drive casing and electronics itself. I have had a few drives where they would work fine in one casing, but not another. Do both external drives work OK on another PC? Could be the way your new PC's usb ports are talking to the external drive's electronics. Hope this helps!