If the refrigerator isn't cool, you need to answer some questions, then see if the compressor is running.
First, answer these questions:
Is the refrigerator completely dead? If so, see “It's stopped completely.”
Is the thermostat knob turned to the proper setting? If not, reset it.
Next, see if the compressor motor is running
The compressor is a football-sized case with no apparent moving parts. It's on the outside of the refrigerator at the back near the bottom. If it is humming or making a continuous noise and your refrigerator is still not cooling, there may be a more serious problem with one or more of several different components, I recommend contacting a qualified appliance repair technician for further help.
If the compressor is not running but you do have power to the refrigerator, there may be a problem with one or more of these:
The compressor
The Thermostat
The overload, relay, or capacitor
The defrost timer
The condenser fan motor