have you checked the mouse port to make sure its connected? when you reboot your pc, does the post complain that no mouse is present?
mice are pretty cheap nowadays so you could try a $7 replacement to see if the cat's finally gotten your old one.
I was using my desktop computer when my mouse suddenly stopped working. I looked in the device manager and the "mice and other pointing devices" tab is completely gone. I restored my computer to a week ago and no luck. Anyone know how to get my PS2 mouse driver back?