[CRASH] - Black screen problems!

Hello people!! I don't know if any of you face or faced this problem but, i get random black screens during gameplay...sincerely i dont know if is a problem from my computer or not but the fact is that i countered this problem only with LOL and no other games. And i have an another kind of bug..After a game is finished and i click continue(when is loose or win) my statistics window wont appear and i have to close LOL and open it again after every single game played... If anyone can help me i will appreciate it...Thank u very much!!