Turn off problem

Hi, everyone. Recently my computer has been restarting after 50 ~ 60 minutes while I'm playing some games (BF4). Ps.: This issue doesn't happen in Rainbow Six. My PC turns off and then turns on again. I don't know what is the cause of this issue, since GPU and CPU temps are no more than 70ºC...

I have a gtx 1080 i7 4790k 16gb of ram system and play at 1440p 144hz. What is going on is I get 60 fps out in the woods 40-50 in some cities and 30 in major cities. I know that it is most likely not optimized however what is weird is its only using 60-80 percent of my gpu mostly around 67...