First, uninstall any special software for the optical mouse under "add/delete programs" under control panel" Then disconnect your track ball and go to "system" under "control panel" and then "device manager". Uninstall any mouse/pointer device and then do the "three finger salute" (control-alt-delete) and restart your computer since your mouse will no longer work. When Windows restarts it should "see" and reinstall your mouse. If you still have the same problem with only one pointing device connected then you may have some corrupt files. This is usually dealt with by reinstalling Windows. If you do all of this and STILL have the same problem then it is as David said...hardware time, usually a motherboard. Good luck.