If your Leapster does not respond to the stylus pen, it needs to be calibrated.
The following are instructions for calibrating the Leapster™ handheld.
(1) Insert a cartridge, turn the unit on and wait for the sign-in screen to appear.
(2) Hold down the Home, Hint and B buttons simultaneously.
(3) When the screen changes, press the A button.
(4) Using the Stylus, touch the center of the targets.