Keep Games in Full Screen Mode

I am playing Assassin's Creed on Windows 7. After I launch the game, suppose I get a pop-up (like Windows Update). Now the game is stuck in windowed mode, and no way to get it back to full screen.

Is there any way to do go back to full screen without restarting the game, or possibly avoid these popups to begin with?


Solution 1:

Alt + Enter is the magic combination to solve your problem.

PS: For Windows only.