Someone please help!!! My mouse automatically highlights items without me clicking on the item. I haven't made any changes to any properties. Normal everyday use and this started happening. The only thing I can think of is I might have clicked Ctrl & ? or Alt & ? to make this start happening. Does anyone know what I might have done?
Thanks,
rmadderra

What sort of mouse is it ? Have you tried resetting its options back to defaults ? Go to control panel, mouse, and have a look in there.

Try uninstalling and reinstalling it. Turn it upside down without the ball and gently tap it on the surface, maybe blow in it , to get all the crud out. Also, use a small brush (toothbrush) and clean around the guides that support the ball. Clean the ball (Windex) You didn't say which model, if it has a scroll ring crud can build-up between the ring and the ball. I have a Kensigton Pro. I love my trackball but they do get dirty
Mark

Also found these troubleshooting articles atMicrosoft