Look in the front left corner behind the kick plate and you will find the defrost timer.
There should be a little knob that you can turn with a screwdriver.
Turn this until it clicks the compressor should start.
If this works you will need a new defrost timer.
Here is a link to the defrost timer for your fridge.
If this does not solve your problem you may have a leak in the sealed system. | 
Freezer not working 
