monitor turns off when I swing rock (still have sound)

Hey,

MY friend is having this problem where he starts up the game and joins a server but as soon as he swings his rock his monitor shuts off… I had him check his temps and they are fine, infact he opened BF4 and had rust open in the back and played for a match then went to rust and sure enough when he swung it turned off and he can only restart his computer to fix it, I had him connect to another monitor… re install the game, drivers, swapped out the ram and also reseated it because he had 2 different kinds and nothing works. anyone know whats going wrong?