Game minimises after launch and can't be brought back up

Every single day at least once. I get through champion select, and then instead of the loading screen with 2 teams the game minimises and can't be maximised no mather what - tried maximising at least 100 times, but it flashes a black screen and returns to desktop. Sometimes it maximises itself, sometimes the whole game goes by and I can't see anything. People keep reporting me for being AFK when in reality I can't do anything. The strange thing is - I have sound, but no actual visual. I do know this isn't my PCs fault, because this happens only once every day, usually the first game, and all other games run ok. Got the laptop a few months ago so it can't be a technical fault. Does anybody have experience with this and could help me? :)
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