Engine will not start with key because it's not getting a trans in neutral signal from the pad transmission.
The pad connector may have fallen off or is so lose it is disconnected. Check this first and you may be lucky enough and just plug it back in.
Also, check the wire harness connection on your transmission to be sure it's properly secured/connected.
Check the entire harness from your selection pad to your transmission for signs of damage or disconnections.
Check your connections on your transmission (TCM), Transmission control module.
If no lose connections are found, I'm sure your pad or your (TCM) will need replacement to correct your problem. An Allison tech will come along soon hopefully and give you more information and real expert advice.
Good luck and please keep us informed.
Dan & Loretta, US Army Retired Aero Scout Pilot
2012 Fleetwood Providence 42P Class A/DP
Spartan Chassis, 8.9L Cummins 450HP