My upward scrolling failed recently. I did a search on the Web and there are plenty of You Tube videos on how to fix it. The first one I viewed was over 8 minutes long and detailed how to take it apart and clean the tiny rollers around the scroll-ball. This is not so easy as the case is glued together, and tweezers are needed as the parts are so small. So, I carried on, hoping to find a simpler solution - and here it is: turn the mouse upside down and roll the scroll-ball around on a sheet of paper. That's it, done, it works!