My computer shuts off mid game and wont turn on until i force shut it down and restart it

shadowslash4

Prominent
Sep 20, 2017
1
0
510
I have a
- ryzen 1800 x
-asus rog strix x370-f mother board
- cooler master 212 evo
-asus nividia 980 ti
-Samsung 850evo 1TB SSD
-750 w corsair cx750m

I just finished building this PC. i reinstalled windows, installed all the drivers and made sure everything was updated. it works fine but when i try and play any game for 30 min or so it will just shut down all processes and turn off the monitors but will still leave the fan spinning for a while after. to restart the computer i have to force shut down before it will let me turn it back on again
I have no idea what it may be my card gets up to 71c and it shuts down. I don't know if it might be the motherboard chip set getting overheated because the card is right over it. i know its not the CPU because the heat sync is still cool enough to touch when it happens but because i have to shut it down i cant get the best numbers because by the time i get in bios it would have cooled down by then