Two wireless mouses in the same room can conflict with each other!!
You should have seen me and DH last nite. Got my new computer all set up and we were both in there, (him on the old one, me on the new one). He kept complaining that his mouse wasn't working and I would stop and look over and it was just fine, so I went back to what I was doing. Then he would say "look" there it is again!! And I would stop and look over and it would work just fine. After about 30 minutes of this we finally realized that when I was moving my mouse his wouldn't work!!
Our computer geeks here at work told me how to fix that, so hopefully that will solve the problem.
But it was kinda funny at the time!!