Unable to do anything at the start of a game

During the loading screen when going into game, i usually alt+tab out to do other things while i wait. However sometimes i can't tab out and for some odd reason, i am not able to move use any keys on my keyboard or mouse. This Happens everytime i tab out of game during the loading screen and it annoys me because i get bans from being afk not being able to do anything once in game for a long while.