PC rebooting in loading screen

So I was in the loadoing screen when my PC decided to reboot itself. Eventually my team remade and I was given a 10 min wait time for the next 5 games. Whats interesting is that the last time (about 2 weeks ago) when I logged on to play a game the same thing happened. After it I was give a repair and thought everything was alright. Sadly its not. My computer has never rebooted itself expect for these 2 particular times I've written about above. Has someone had the same issue or know something about?! Thanks for the responses!