Cause: You haven’t synchronised the device properly.
Solution: There are three ways you can get the mouse to work. First, press the Connect button on the mouse itself, located at the bottom. You’ll need to use a pen for this. Second, press the Connect button on the USB receiver. Third, go to the Mouse Properties in the Control Panel, and on the Cordless tab, click Connect. One of these three should solve the problem, and your mouse should get connected.