GAME MINIMIZING!

Over the past 2 weeks, 2 separate computers I have are experiencing a minimizing effect at around the 2-4 minute mark in every single game. One computer I've had for years, which could have other issues by itself. The other one is BRAND NEW. Like, I built it; I installed windows 10, antivirus and League of Legends. It has the exact same problem. I'm at a loss, because 2-4 minutes is like the first trade window and I always lose because League minimizes for 10-12 seconds at the worst times. If you have any ideas or suggestions I'd love to try it out.