Question:Why is that my PC is not reading my A: prompt (floppy)?
Answer: The first thing I would check is to make sure the light on the floppy drive comes on when you try and access it. If not then this is your first sign of trouble.
If you are getting error messages I would try different disks. Floppy disks are known for going bad easily. If it does it with any disks then it is a very good chance your drive is bad. I have seen them go bad many times before. They are easy to replace and only cost around $25. If you want to try replacing the cable first then that would be an easier, cheaper starting point.
If Windows sees the drive but it can’t read disks then it’s most likely the drive itself. If Windows doesn't see the drive then it could be the drive, cable or motherboard setting or port.