when you switch it on does the compressor try and then click off.I don't think it is the compressor you hear I think its the air fan inside whirring away.now to help you fix it.
If you go around to the back and look at the compressor then look slightly to your left and you should see a plastic square box mounted to the back wall.in the middle you should see a round cap.prise off cap.under there is a defrost timer.put a flat screwdriver in to the hole and rotate it clockwise and see if the compressor starts up.if it does then the defrost timer is faulty and needs replacing.around £10
ck
January 2010