Diagnosis
Loss of power to the wall console. The low-voltage wire running from the motor unit to the wall is disconnected, cut, or shorted.
How to Fix It
Check the terminal block on the back of the motor unit. Look for the two screw terminals labeled for the wall control. The thin 2-wire cable from the wall should be firmly under these screws. Tighten them. If that's good, trace the wire from the opener to the wall. Look for damage, especially where it might be pinched by the door track or staples.
If That Didn't Work
The wall console itself is faulty. Disconnect the wires at the back of the dead console. Touch the two bare wire ends together briefly. The opener light should flash. If it does, the console is bad and needs replacement (Chamberlain part #41A5021).
Heads Up
Do not splice the wall control wire with electrical tape. Use a proper wire nut or solder and heat shrink. A poor connection can cause erratic operation.