My Samsung G600 has stopped working

This would mean that at sometime your phone got wet by some form of liquid.I don't know if u could do this but the phone needs to be opened and your keypad needs to be lifted(the one on the pcb or main board) and cleaned thoroughly by a spirit solution that would evaporate and then replaced.you'll have to clean the pcb side and the contacts on the actual keypad and that should do the trick hopefully.try not to disturb the adhesive on the keypad because you would need to reseat when u r finish cleaning. thanks !

sam !