....swapping in a PS2 mouse and testing it? If it works correctly, then the problem is probably an issue with the mouse, or mouse software. If the optical device is malfunctioning or the mouse software has become corrupted, then a regular PS2 mouse should work fine.

You could try uninstalling, then reinstalling the mouse software and see if it helps, but if the mouse if faulty, replacement is the answer.

Hope this helps.