You might also check for new drivers for your mouse - I ran into this problem on my old Win 98 computer, even though it was the same wireless mouse I'd had for a couple years, it suddenly quit, and after a consultation with the Bro-in-law, I went looking for new drivers and after downloading what appeared to be the right one, it worked fine. Vista, however, says it has its own drivers, and did not want anything to do with the mouse's software. I just plugged in the receiver/transmitter thingy and it worked immediately.

I love my cordless mouse. I use rechargeable batteries, and it's one less wire for the cats to play with or me to tangle up in.