[Client] User Kernel Quit Unexpectedly

My league was not working so I deleted it, then downloaded it again. But this time sometimes it works but sometimes it gives me a little tab telling me that user kernel has quit and when I reopen it comes up with the same thing. A way to get this is to download league again and do what it tells you but then open it in the applications. The league splash art should show up but then this does; sorry but I don't know how to add a screenshot.