you can try with 2 hands put some pressure on the ADB keyboard plug, dunno up,down,left,right at the same time tap on keys or wiggle the mouse... or wiggle the port while wiggling the mouse. see if the cursor moves at all...

nice thing the ADP is plug and play.

i had a LCII i was playing around with, i was pinching the capacitor cans to try and make the sound not squeal, i ended up pinching the ADB can because mouse and keyboard stopped working, i was lucky i pinched the can the opposite way and it the mouse and keyboard came back, so at least i do know with the LCII there is a cap that could keep the keyboard from working.