Thanks for the help. But it's not working. I still can't switch between window and fullscreen.

The only reason for me to turn into window mode is because, if the game somehow gets alt-tab [minimized] and then if I return to the game: it turn into window mode automatically.

But in this case, there's no window resolution available. So the screen gets black. I can still press "alt+enter" to turn it to fullscreen. But the screen still remains black and only way to fix this is by restarting the game.