If you know the freezer has electrical power because the inside light turns on, but the compressor won't run, a failed cold control thermostat could be the problem. To determine if the freezer temperature control is working, unplug the freezer and check for continuity from the power cord wire to the compressor wire at the control. If your meter doesn't measure continuity between those wires, then you'll likely need to replace the freezer temperature control because it isn't sending electrical current to the compressor.
If your freezer has electronic controls instead of a dial, a failed relay on the electronic control board or a bad control panel can prevent the compressor from getting power.
If the compressor is getting power from the cold control thermostat or the electronic control board, a failed start relay on the compressor may be keeping the compressor from running.
If you hear the compressor clicking constantly about every 30 seconds but the compressor motor won't run, the compressor pump may be locked up. The clicking noise is caused by the overload tripping when the motor overheats because it can't spin the locked up compressor pump. Replace the compressor if it won't run when activated. A service technician will need to replace the compressor if it's bad because that repair requires recovery and recharge of the refrigerant.
