Pat,
The more likely problem is that a connection vibrated loose. You should verify each connection in the AC circuit.
If you have a multimeter,
disconnect the power and check the resistance across the AC heating element. If that's open, the heating element is bad.
With the thermostat set to maximum, check the resistance across the thermostat (black to white). It should read zero ohms. If not, the thermostat is bad.
If the thermostat is not switching power, it could be that the capillary tube is broken. The capillary is an integral part of the thermostat and is a very skinny tube leading in to the back of the
refrigerator to a capillary bulb which senses temperature. If that tube is broken, the thermostat will think it is very cold in the
refrigerator.
If you replace the thermostat, be very careful to not kink the capillary tube on the new one.
This schematic will help your troubleshooting: