Fridge never stops

Most likely that the thermostat is defective or the main controller board is defective. Try powering off at the mains and leaving it off for 30 mins and then turning back on the power - it sometimes works. If not then call in a repair man asap.

How to check everything
http://www.acmehowto.com/howto/appliance/refrigerator/refrigerator.php
If the evaporator coils behind the back panel of the freezer are icing up because of auto defrost failure that will stop the circulation of cold air and eventually affect the freezer too.

check defrost timer, defrost heater, defrost thermostat. In most newer models the timer has been replaced by an electronic control board. If the heater and thermostat are ok it’ll be the control.

You can turn the defrost timer till it clicks and everything shuts down. The heater should now come on. If it does, replace the timer. If it doesn't, check the heater and defrost thermostat. Turn the timer again till everything starts back up to end the defrost cycle.