A drive can be any letter from A-Z, but A is taken it is default on floppy drive's, mainly because floppy drives were one of the first creations to PC's after Mem sticks. Beside the point, you just need to find the correct letter and place that as the root point and try again. Also the error could be a disk all scrached and miscondition, I had that error once when a disk had a crack in the middle. So maybe its not just the Letter, and a ribbon cable could be loose, or damaged, or the PC is just very.. how do i say, Fairly damaged.