We changed the batteries and Madison's Leapster tonight. However, the pen/stylus quit working. Here's how to fix it:
1) Ensure that a cartridge is not inserted
2 (aff)) Hold down the Hint button while turning the unit on
3 (aff)) When the LEAPSTER menu screen appears, press the A button
4) Touch each of the crosshairs that appear with the stylus
5) Restart unit
I'm listing it here for others and for myself, if it happens again.