Can't tab into League

Just recently I've encountered this problem, I've tried to get into a league game twice now, and both times as soon as I tab out to play some music it black screens and doesn't let me connect again. Last time I had to restart my whole computer, this time I just couldn't tab in and it was a remake both times. This has caused me to lose loot privileges which is extremely annoying considering when I logged in I got free loot for being honorable... Please help :( I'm scared to go into another game.