My Magic Mouse stopped working, I charged it (I thought), but it is still not responding.

The following will require any USB keyboard and mouse. If you don’t have them, borrow or buy them, they are inexpensive!

1.     Connect the USB keyboard and mouse to the computer.

2.     Open System Preferences – Bluetooth

3.     Un-pair the wireless keyboard and mouse.

4.     Turn off Bluetooth

5.     Restart the computer in Safe Mode per the directions in How to use safe mode on your Mac - Apple Support

6.     Restart the computer normally.

7.     Open System Preferences – Bluetooth

8.     Turn on Bluetooth

9.     Re-Pair the wireless keyboard and mouse.

10.  Unplug the USB keyboard and mouse and begin testing the wireless devices again. 

have you tried turning it off using the switch on the bottom, wait five seconds, and turn it back on? then try clicking the mouse a few times while moving it and see if it wakes up?

I had the same issue. Using another mouse remove the non working mouse from the Bluetooth pane and then add back in