Have you done a battery reset? If not, remove the battery, reinstall and see if that fixes the problem.
If that does not work, remove the battery and then press firmly on the trackball and move it round and round. This "cleared" my trackball when it stopped moving the cursor. I assumed there was some kind of obstruction inside.
You can also get some alcohol or Windex, spray it on to a paper towel and rub that round and round on the trackball. Then move the trackball round and round as described above. Do NOT spray the Windex anywhere else or directly on the trackball!!!! Spray the towel.
If that does not work, you can call tech support and make a warranty claim.
If you want, you can disassemble the trackball, clean it up and see if there is anything in there that might be causing the problem. Keep in mind that if you break something, then the carrier will not cover the defect under the warranty. So the choice is yours.