Client Issues

Hello there i have ran into a issue with the client and game. While the client is open it will flash sometime and then the lol icon will appear a load of times on the taskbar then Disappear instantly (also happens when i click the client). Once im in game if i Alt+Tab out i cant Alt+Tab back in but i can use Task manger to switch to the game again. Please help this has been killing me i was on the phone to Microsoft and goggled for hours trying to find a fix

Cri evey tim