Cant minimize the game

Hi guys, I got problem where I cant minimaze the game while its loading or while im playing. Before, I just had to press the windows key, that doesnt work now, nothing happens. So I tried CTRL+ALT+DELETE, which opens the windows options, but if I click one, I get a black screen for like 10 seconds and then it puts me back into the game/loading screen. Which sucks, because if someone sends me a message on steam, I cant answer him or if I was watching a video on youtube, I cant stop or pause it, it wont let me. So my only choice now is to leave the game and reconnect when I want to do something on the desktop. Got any tips?