When I close lol he doesn't close, it stays in the Task Manager... Need help !!

So... I open lol e start a game, the screen blacks out, and then it closes, and says bug splat, then I try to close lol and it doesn't close so I go to "Task Manager" and I try to finish task. Lol launcher closes, but in the Task manager it stays open a task of lol... And it doesn't close... I try to open lol and it doesn't open... Then only like past maybe 20 mins it closes and i can play again, I tried to reinstall, but it didn't do nothing... I think its because of the new client, because i didn't had this bug with the other client... help me pls...