Probably originally a loss of refridgerant gas and because you are still trying to run it even though it is not getting cold (which is a pointless waste of power) you have more than likely stuffed the compressor motor (the black pot as you call it). I say this because you say that the compressor is very hot & buzzing. Call in a service company or just go and buy a new fridge.
Lincoln Appliance NZ, June 2009