Game constantly minimizing during match

RCooper

When I play a match, within next 5-10 minutes the game would just minimize on its own, a few seconds before that it would freeze. Then the focus changes to another window on my Windows, like file explorer or browser or Discord. Then I have to manually change the focus back to the game window. And then I can play normally again. But within next 5-10 minutes same thing happens again. It is really annoying especially during important moments when I am left alone in the team. What can I do with it? 

If I only have Crossfire opened without any other application window on the background, my computer would just freeze and I wouldn't be able to do anything except to restart my computer anew.