Shifting focus away from Maple

I used to be able to change screens by pressing Alt+Tab. From around August when I do that I either get a black screen or I can go back to Windows fine but when I move focus back to Maplestory I get a black screen (usually the latter). I left the sound on yesterday and it turns out the game hasn't crashed; just the video is completely black. Alt+F4 doesn't work but after returning to the log-in screen using Esc+up key+Enter, I was able to close Maple using Alt+F4. Is there a way to fix this?