I'm guessing you mean that tapping the library button isn't getting you out of the store.
Try powering the device down. Hold down the power button for about 3 seconds, until the power off slider shows up. Slide it. After the iPad finishes shutting down hold the power button down again, for about three seconds. The Apple logo should appear and the iPad will restart.
If that does not work, do a soft reset.
Hold down the power button and the home key until the Apple logo appears. This will take 10 to 15 seconds. The iPad will reboot. This takes longer than the restart, so don't worry. Should take anywhere from 2 to 5 minutes.
If that does not work, call Tech Support.