Previously my mouse was working fine on Ubuntu 10.04.
Now, starting today, it stopped working. I tested with 2 other mice, but it's still not working. The mouse is turning on though, I see the lights on the bottom.
The mouse getting lit up means there's power, but not necessarily that you have communication with the system.
I'd probably start by checking if X actually detects the mouse with
If both of these work, this might be x config related - maybe create a backup for your xorg.conf file if you have one, and create a generic one with
It might also help if you knew what exactly happened before it stopped working.
You might get some ideas as to what else to poke at from Ubuntu's X input config page