black screen

while playing league of legend by using laptop, after I kicked my power line from laptop's electrical socket by my feet under mistake, the screen became dark. But, the game still running as i can hear the sound from game. I believe this happened few times before, and, the screen keeping dark not matter what I do, even I click Tap-Alt. Therefore, I have to turn off my laptop, and I receive my AFK punishment. My laptop is Dell, cpu 2830,64-bit,windows 8.1.