I just had this problem happen to my Amiga 2000 out of nowhere too. The mouse was working, then it wasn't. No light on my Tom+ adapter and no movement (but the buttons work) when I plug in a regular Amiga mouse. I've got a voltmeter but no probes fine enough to not short out every pin in the DB-9 connector.
I think I've got an old PC serial mouse I can use SERMOUSE with until I figure out what's wrong.