My league of legends keep crashing

Hello there, so my problem starts when i bought my new pc, i have got a Intel(R) Core(TM) i5-3570 cpu @ 3.40GHz, 3401 Mhz, 4cores. motherboard from AsusTek Computer INC. version Rev X.0x, 16 Gb ram ddr3, a gtx 980, and that's all you need to know i think, more briefly i'm in game walking to my lane doing my farm or fighting, and then bum my screen went black which I could solve the problem by pressing ctrl + alt + delete and then press cancel but after a couple of minutes happens again, and i need to restart my pc bc u need to press quickly and it's random. It's not something that happens for a specific reason like killing a wolf then crash, it's completely random, i was thinking it's my cpu's problem but i've checked online if my cpu is broken, but it wasn't it works fine. When i'm in PUBG works with 60 fps constant, same with Far cry New Dawn or Far Cry 5 which are games that a broken cpu can't handle, and a lot of games like these 2, I forgot to mention that this thing happens without any bugsplat.