Here are your parts
Here is the tech sheet and a service manual with operators manual
First try to get rid of the lock. See page B-9 in Operators Manual
Next thing I would try is disconnecting power from the unit for half an hour or so. Sometimes the electronics can lock up, the above may reset them
Next try the diagnostics
Next try cleaning the ribbon cable re:Control Panel
RIBBON CABLE CLEANING
Unplug the unit
Open it up
Remove the ribbon cable from the keypad to the control board at the control board.
Clean the edge connector.
If it is the type where there is not a connector just the insulation is removed, it can be cleaned with a pencil eraser. Do not use an ink eraser as it is too abrasive.
Check the tracks in the ribbon cable for hairline cracks. A magnifying glass helps here.
Would not hurt to clean the connector on the board. Use electronics contact cleaner or isopropyl alcohol and a tooth brush. Be gentle and do not reconnect till all the solvent evaporates.
Reconnect everything and give it a try.