Ok if you cannot hear the compressor running then its going to be either the thermostat faulty of the compressor.
To check this you need to remove the light fitting inside the fridge and in there is the thermostat. It may have either 2 or 3 wires going to tags number 3,4 and 6.
Now you will need a multi meter to test this so turn the thermostat on to a number and then test between tags 3 and 4 and see if you have a reading. If you don't then the thermostat is faulty and will need to be replaced.
If the thermostat is fine then this will be a compressor fault which for this it isn't a diy fix as you will need to get a fridge engineer in as they will need to regass it once the compressor has been replaced.
So check the thermostat out if you can and see what you find. If you need anymore info just get back to me.