It's interesting that someone should mention a mouse.  I've had a lot of trouble with my mouse lately.  I tried everything I could think of.  I eventually changed the ball and it works fine now.  Not being computer savvy, I only found this out through extensive trial and error.  For the benefit of those of you who may not be up on this, if a mouse fails to operate or should it perform erratically, it may need a ball replacement.  Because of the delicate nature of this procedure, replacement of mouse balls should only be attempted by highly trained personnel, as I found out the hard way.  Before proceeding, the replacer must first determine the type of mouse balls by examining the underside of the mouse.  Domestic mouse balls will be larger and harder than foreign balls.  Ball removal procedures differ depending upon the manufacturer of the mouse, but typically, foreign mouse balls can be replaced using the pop-off method and domestic balls are replaced using the twist-off method.  Contrary to popular belief, mouse balls are not usually static sensitive.  However, excessive mouse ball handling can result in a sudden discharge.  Therefore, I highly recommend wearing safety glasses when handling mouse balls.  Upon the successful completion of ball replacement, the mouse may be used immediately.