Since at least the last patch my keyboard input will be normal for the vast majority of the game, but without warning, the game will just stop responding when I try to use any/all of my abilities. This is very frustrating and can be (and has been) game breaking. It usually goes back to normal when I press Esc, but has been very problematic for normal gameplay.
I encountered same thing are you using windows 7? If ya this fixed the problem : http://windows.microsoft.com/en-us/windows-vista/troubleshoot-keyboard-problems
Like your keyboard decides nothing works on lol/ other games but on google chrome you can do something... Its a windows problem as I know more than league but still annoying caus ya cannot spam any ability, you cannot leave game caus esc doesnt work and you cant tell your partners what happening because you cannot write anything so you jsut restart your computer? :P
