My USB backup disk some time ago had a malfunction. I finally reformatted the disk, losing many iterations of backup, but I thought it was working. I see now that it has not backed up since Dec. 12. Neither the Macbook Pro's 2.0 (I think) USB drive, nor the 3.0 (I think) on the external keyboard notices the backup drive. (Built-in keyboard doesn't work, hence the USB external keyboard.) Why and what to do?