Webba, I'd check two things:
1. Is it clean inside? I don't mean drop the ball out and clean it, I mean remove the screws and take the lid off. You will probably find all sorts of fluff and crap inside. Get it all out with compressed air at the local garage. Make sure that the little wheels all have clean slots. Make sure that the shafts on which the ball rides are clean, not covered in hair and fluff.
2. While you've got it open, plug it into the mouse port and check that rotating the wheels by hand (gently) moves the mouse pointer up/down and left/right. If it doesn't. I'd think about cutting off the end of the cable a few cm away from the mouse and re-terminating the cable. But that's a bit drastic if you don't have the proper tools.
tony
