mouse wheel stopped working

Hey people I recently about the new iMac about two months ago...
I'm having this really annoying problem: the mouse wheel won't scroll down! It scrolls up and sideways but not down, it doesn't make that fast clicking sound when scrolling down (although it should). I've had this issue before and to correct it I moved the wheel in circular motions until it would start scrolling down again.. but now its completely dead, no more scrolling down for me

any ideas anyone?

*Moved thread to appropriate forum - Question not on iMac but Mighty Mouse*

You might want to try these suggestions, How to clean your Mighty Mouse.

How old a mouse is it? From description of moving the ball maybe it is a take apart mouse with the washable ball?

I use either a dry or damp cloth to clean the mouse ball.