damaged PS3 over heating problem

HI can anyone help my so called better half dropped my PS3 slim got to turn the power on and off about 10 or more times before i can get a signal on Tv when i do finaly get it going olny able to play 2 games at most then screen freezes got to start all over again turning on and off. sent it off to be repaired but they said due to over heating it cant be repaired. Would that be the mother board if so could you tell me where i could buy one and how much it would cost its a 250G model or would it be easy buying new consloe thank.Baz UK