Prentke Romich Company
http://www.prentrom.com/support/article/336

Why Won't my Liberator Accept Switch Input?

Assuming that you don't have a bad switch, cable, or port on the Liberator and your Selection Technique menu is set up properly, you may need to do the following reset (Called a "Warm Boot").

1. Unscrew the battery pack screw one half turn, counter-clockwise.
2. Slide the battery pack out until you see the battery telephone cable.
3. Unplug the battery cable.
4. Plug your battery charger into the battery pack.
5. On your Pathfinder, hold down the OFF button.
6. As you are holding the OFF button, plug the battery telephone cable back in. DO NOT let go of the OFF button.
7. As you are holding the OFF button, push the ON button as well.
8. In about 10 seconds you will hear a beep.
9. When you hear the beep, let go of the OFF button first, and then release the ON button. 
10. Watch the screen, the Liberator should power up normally and show "System is Ready for Use."
11. Now go to the Selection Tech Menu [I2] and select (#3) Setup switches. The switch should now be accepting input.
    

Note:  Doing this procedure will NOT erase your memory.