I a suggesting cleaning your trackball, the steps and information along with pictures will be provided below. I followed these same steps and mine works fine. Trackballs can easily accumilate dirt and dust over any period of time.
First, you'll have to use the screwdriver to remove the ring from the outside of the trackball. I'd recommend doing this from the top, since it's the only part of the wheel that doesn't have a prong (you'll see what I mean when you pull it out). Once that is loose, you'll be able to take the trackball unit out as well. The set should look like this:
Now we want to concern ourselves with the trackball unit. First, wet your finger and run it across the trackball to pick up any residue which might be sticking to it. Next, you'll notice there are four black wheels on each corner of the unit. Remove them one by one, removing any dust or buildup with your fingertips. I'd recommend not using water here. Just something about water and BlackBerry
that makes me uneasy.
Finally, we'll look back to the unit, where you'll see a copper sensor where the trackball used to be. Wipe this gently
with the rag. This is a very fragile and very sensitive part. If you treat it roughly, it will break and you'll have a worse problem than a dirty and clogged trackball.
Finally, drop the trackball unit back into the crevice, and pop the ring back on, prongs facing left, right, and down. Voila! Should be good as new. And now you don't have to send your BlackBerry to IT, or out for repair. Now if this does not work, you can order a replacement trackball from ebay for less than 3 dollars and just use the examples above to install it.