clean up your scroll ball
I had same problem with my Apple Mouse (wired version) and found solution on this website. It worked instantly! my mouse is now alive!
http://www.askageek.com/2006/07/26/apple-mighty-mouse-click-scroll-wheel-wont-scroll/
Q: I just got an Apple Mighty Mouse and all of a sudden I cannot scroll pages down but I can scroll up and to the side with my Apple Mighty Mouse. I cannot find a way to easily take it apart and since it is only a week old it does not make sense that it is broken. Could I need to clean it and if so how would I go about cleaning the clickable scroll wheel?
A: It is actually pretty common that the clickable scroll wheel on the Apple Mighty Mouse stops working like that because people use the mouse for hours and hours a day and their fingers have oils and dirt on them and it gets into the clickable scroll wheel. Remember when you used to have a mouse that had a wheel on the bottom, most people have lasers these days but some people still have the wheel, and you had to take the bottom off and clean all the rollers inside the mouse to make the mouse track correctly?
Well it is the same idea behind the clickable scroll wheel except, like you said, it does not seem like it is easy to take the mouse apart and even if it were easy I would not suggest it.
The first step to getting the clickable scroll wheel clean is to get a dry hand towel and use it to roll the clickable scroll wheel all different directions. This will get the dirt and oil off the ball and off the sensors that it touches. The good news is that in most cases this alone will resolve your issue. If you find this does not resolve your issue then you will want to take a damp cloth and do the same thing.
Now people, damp does not mean running it under the sink then walking to your desk and dripping all over the place as you go. Damp means a few drops of water on the cloth then ring it out and make sure there are no drips. You will want to rub the clickable scroll wheel a few times and then dry it off with a dry part of the hand cloth. We can do this because we did not get the whole hand cloth wet right
Good luck and enjoy your Apple Mighty Mouse because I know I do. For those of you that do not know what an Apple Mighty Mouse is visit the website here at Apple Mighty Mouse.