Turn it upside down and desolder/resolder the connections of the micro switches at the front of the drive. There should be two of them, one on each side - one is the read/write protect sensor switch and the other is the floppy lowered in drive sensor.
With your fingers, spin the disk on the bottom of the drive and see if it is not stuck. It should be fine in 99.99% of the cases but sometimes dirt and crap can get in there and needs to be cleaned out. You could blow it out with compressed air.
Edit: Also, after soldering, spray from WD40 or some other spray oil into the switch to clean it through the pin and hole on the top of the switch. Wipe it dry with a paper towel when done.