WIndows 10 Random Black screens?

So after i built this pc.
It only happened 2 time in 1 months (basically once a month)
When playing League of Legends the screen would go blank and i would hear throught headphones that something disconnected(the windows disconnect sound). It would appear again after 15 sec, but league would be like green screen and would not respond so i would have to to terminate proccess in task manager.
Now i use 2 monitors and one of them is tv/monitor. And the main monitor has an adapter bcs my main monitor doesnt have the displayport.
Could this be the graphics card or the adapter?
The adapter is display port to hdmi.
It appears as not the main but my second monitor disconnects causing the trouble.
All help is appreciated!