Comp Blackscreen

I need help. My computer will freeze while I am playing a game for about an hour and then my monitor will turn black and my Keyboard and Mouse will turn off as well, however my CPU and GPU are still spinning and my led fans are still alight inside my PC. I then have to unplug my power supply as the power button also stops working then restart the computer all over again. I dont know whether this is a problem with my motherboard or power supply.