PLEASE HELP! KEEP CRASHING!

Hi guys, please help me out. I dont know why but for the past month my games have begun to randomly crash aswell as freeze up my entire pc, and the only option is to Ctrl+Alt+Del and log out of my pc, then back in and start LoL again to reconnect to the game. I've tried a repair from the client, and it worked for a few days, but then it started again.

Does anyone know the cause of this? It sucks when a teamfight is about to begin and i suddenly crash and dc. Another thing is that it used to only happen once a day, so when it happened I'd be at ease knowning it wouldnt happen again in my games for the rest of the day. But its recently started to crash twice in one day, which is scary D: I have a good gaming PC too, running League at about 100 FPS+

Please help me, thanks!

EDIT: It always makes a bugsplat sound when it freezes, if that helps, but nothing pops up, just a complete freeze.