I am not sure how you are determining that your refrigerator is stuck in the defrost mode. In this mode, the compressor will be off and the circuit for the defrost heater will be energized. The defrost bi-metal thermostat will be open to interrupt this circuit if the temperature is above 55 degrees. This thermostat will not reset until the temperature drops below 20 degrees. If the refrigerator was cooling properly and then went into a defrost mode, the heater should have shut off if the temperature in the evaporator area rose above 55 degrees. The control board will normally detect the opening of the defrost bi-metal. It will not immediately start the compressor after the bi-metal trips. If the condenser fan is running but the compressor is not running, then you have a problem with the compressor, the start relay or you have a wiring failure that is preventing the compressor from running.
If the condenser fan does not run at all then the control board could be bad. We would need to have more details to help you diagnose and troubleshoot this problem.
You may need to have a service technician physically examine and repair the refrigerator. Here is a link for the Sears Service website in case you need it:
Sears Home Services