Random Crashes in games

For about a year I am Getin random crashes of my whole pc while I am playing league of legends it doesn't heappends in every game but like in 1/5 games. First of all I though my procesor wasn't good enought, I brought a new one (i5, gtx 960 graphic card, 8 GB ram) and still I was getting those crashes I tried to uinstal league but didn't work. Can somebody help?