When I press on the Play button and when I am in the menu of the game (with buttons like Singleplayer, Multiplayer etc.) and then I press F11, Minecraft gets bigger but I can see through it. I can't see the game, I can only see my desktop through Minecraft. Thanks!
Take a look at the comments in MC-2067. This issue may be a duplicate of that one, and the information there may help you resolve the problem.