Last night, my mouse left-click stopped working.
Cursed, changed batteries (wireless mouse) no good.
Tried another wireless mouse, batteries were dead, no spares arghh!
Shutdown (Ctrl-alt -F2, it’s a Linux box) and went to bed.
This morning, dug out spare USB mouse from parts bin, booted up- no left click!
Then I noticed that my spare (metal framed) glasses were sitting on my Wacom tablet, which uses a magnetic field to detect the pen- Doh!