GTA 5, Just cause 3, the whitcher are all cpu intensive games, if the cpu gets to hot it will lag the game trying to cool its self, if it cant do that it will shut the computer down.
A display driver crash will kill the game and drop him back to the desktop not reboot the computer.
Once again everyone is guessing till we know what his computer specs are.
EDIT for new info
Im leaning more to the PSU now that i know its a VS, What temps are you getting on the cpu during gaming?