How to fix my unresponsive Magic Mouse

Agree 100% with stedman1. I use non-Apple laser mice yet have had a single hair stuck in the laser window, not obvious in a cursory exam, cause similar effects until removed. Inspect with a magnifier if needed.

At this moment there is a single hair in my trusty old Logitech mouse. The hair moves in and out of the laser window as the mouse moves and, when in the window, is only apparent as a glowing "wire" when the mouse is is powered up:

Also try different work surfaces. Highly decorated mousepads with high contrast variations in the printer pattern can trip up some laser mice, as can semi-transparent or shiny surfaces.

It's surprising how many mousepads are still sold that are better suited for old-school roller mice rather than modern laser mice.

As strange as this suggestion may sound: carefully check the bottom of the mouse for any sign of lint, hair, etc.

When my mouse was acting up, I was able to clear a small, very fine hair, from the outside of the lens using a damp Q-tip.