Hooray! Another ball-mouse user!. This happened to me a few times before, and heres what I did.
Cleaned off the ball( make it look new, no hairs or dust!)
The rollers( where the ball contacts the mouse, they roll...lol) usually have a nice amount of clumpy-dust and dirt on them, use a toothpick or a pencil to get that ring of uglyness off.
Then check your connection and try it out.
f the rollers are moving when you move the ball, and it still doesn't work, then go buy yourself a new one. Thats all I got to say.