Wired Mighty Mouse Not Working Right

I've had my iMac for almost a year now. It came with the wired Mighty Mouse, and now it's not working. I am back to using the mouse from my old PC. I,looked into the settings for the mouse in system preferences, and it seems that whatever the middle button(button under scroll wheel) is set to is what every button does, no matter what each individual button is set on. So if the middle button is set to Primary, everything button will be primary, etc . . .
Is there anyway I can reset the mouse, or reinstall the drivers for it, or something? This is driving me CRAZY!
By the way, I'm on Mac OS X 10.5.4 . . .

Try setting it to Dashboard.

Hi...this may sound simple but my scroll button on my mouse sometimes stops working and it may be because it's dirty. If you fold a post it note so the sticky side makes a triangular point....then poke it aound the ball you will see lots of muck come out...try it a few times and see.

try this a few times and hopefully should start working.