I have a directx 11 card. When i try to enable the directx 11 mode by setting "true" to "false" the game can only be played in windows mode. Pressing alt and enter has no effect.
This may sound a bit odd but did you make sure your mouse pointer was actually in the window when you did alt enter. I only mention this because I have to do the alt enter trick each time I play. Everytime I launch I wait for the game to start up, I move the mouse pointer into the windowed area, and I left click once before I do alt enter. I used to have the same issue until I figured this out. Hope this helps!
simple but true, to be honest i dont even know if mine runs in DX11, i have 2x card that support and w7 ultimate ect ect and i just whack everything to Ultra and run @ 16.10 at 1080p (1920x1080) ?
but the click the window before alt enter is spot on too