i went through this with a brand new motherboard ... very annoying ....Could be the Floppy drive controller ....
If you have just put a new floppy drive on the PC ... try reversing the cable on the floppy drive end........
If the floppy drive light is staying on ,the cable is on wrong.. also any disk in the floppy at the time will be corrupted....
On the cable are redots = pin 1