LoL keeps crashing my PC

Hello everyone, As you can read in the title my computer keeps crashing when i play LoL. It always happens when i start a new game, after like 10 min. my Pc just restarts. The Screen turns black and it says: ''No signal''. After a few seconds it restarts and i try and reconnect to the game, it always works but after a few min. it just continues crashing. It crashes multiple times, my record is 6. I have Windows 7 and my LoL never crashed before but it started a few days ago since then it does that everytime i play. Like i said it never crashes in the launcher or the title screen, always when i'm in a game. I repaired the Launcher, de-installed it and re-installed it, cleaned my PC, looked for Viruses, changed a few settings of my PC, so far nothing has worked. One of my friends who also play's League never had this problem and he tried to help cause he really knows alot about computers but even he could'nt help me. I've read alot of posts where people complain about the same thing and alot of players tried to help and tell things they could do. But then again there are people who comment they tried all of those things and nothing has worked. I'm so frustrated, i wanna play ;_; I don't know too much about computer and hardware and all it's pieces so i think i'm lost. I don't think it has something to do with my PC cause it could run much bigger games. All those people are talking some weird Tech stuff like 'BIOS' GraKa' and i don't know clean your computer from the inside or something. TBH i'm not a technician, i'm just a girl that doesn't know shit about computers. This Computer belongs to my dad, he doesnt care... He says:''It never crashes when i use it cause i don't play games like you, so i dont really care.'' Well he will care when i throw his PC out of the window. (jk i won't do that XD) PLEASE! if anyone has an answer to this then i beg you tell me and explain as simple as possible. XD Here have Ahri :3