PC suddenly crash and say no signal but still runs but no display

I have been experiencing this for a while, whenever I try to play games, and suddenly it crashes, but pc is still on, but no output on the monitor so I have to shutdown it down using the power button. When I check the event viewer it always just says The system has rebooted without cleanly shutting down first. This error could be caused if the system stopped responding, crashed, or lost power unexpectedly.