Ignoring the fact that you've tried an A2000 disk drive and assuming it's a physical problem with the A3000 drive - take the top off the drive and look to see if there are any foreign 'bodies' in there.
A long time ago I had a floppy drive that wouldn't read disks and found the problem to be a dead moth that had crawled inside and got squished between the worm drive and read/write heads (serves itself right I say!).
