Problem with A:/ drive

[JohnR]

Either the cable is not connected (common when someone takes it apart) or it's disabled in BIOS

Another thing to keep in mind. Unlike laptops, desktops usually don't have anything to secure their internal cables. It's fairly common to have parts back off and have poor or no contact. Likely that the floppy cable is not seated in properly, on both sides. Good practice is to pull the case off and confirm everything is tight (stay away from the CPU unless you're familiar with those) after moving PC around a lot...