having an issue suddenly

[riotttcore]

So i have been playing nonstop since i bought the game with no issues but suddenly within the last hour or so i have a huge issue. When i play it will randomly leave full screen to where i can see my taskbar and then go back into full screen but i have to click the screen to go into the game and i can run again but then it pops out and keeps repeating this. I have changed nothing and yet this is suddenly happening. anyone have a fix or similar issue? The game has suddenly become unplayable.