Trouble with Brother Desktop Publisher

[richard123vmt]

The trouble is it shows defective floppy disk message. The disks are good and not write protected.
I have two machines, a DP530 and a DP 550. I can hear a sound from the floppy drive on both. I have verifed the drives are identical and have tried switching them resulting in the same error message on both. I am pretty sure the drive in the 530 was good, but now I get the message on both machines with either drive installed.
Is there something that can be wrong besides defective floppy disk or drive? Is there some reset I should be doing? Any help?