Black Screen during game that made me restart my computer.

Today I was playing ranked and half way into the mid game my computer's screen just went black. Normally I would just press the sleep button (Fn+F1) And I would wait for it to go to sleep, except it didn't, so I had to restart it. I had a friend in the game and I messaged him to hold the line, and they couldn't so we lost.

My question is, where can I report it so I don't get a penalty for it? I know it's my fault for having a crappy Acer, and I really wished the screen didn't go black so suddenly.

If I have a get a penalty for it, then I'll have to endure it (Unfortunately)

And also, how do I fix the Black Screen problem? it has happened multiple times and you don't know how many times I got it during an important moment in the game.