Alt tab glitch

If you alt tab out of the game right when the actual game tab opens and you see the league of legends icon open in the middle of the screen the game tab will go black and you cant open the tab and play. I have found no way to reopen the game and ive had to be a leaver due to this two times so far (my Nocturne game and my Darius game if its still there ) and the only way to get rid of the tab and the icon is to completely restart my computer, this hasn't been a problem in the past and its just started occurring this week.