Strange Game Launching Problem (Notebook)

I am using notebook which is connected to 27 inch monitor. Normally I could play without monitor from notebook screen. Yesterday I have connected it again. When I play from the monitor no problem game starts but after close the monitor and want to use only notebook I got white screen (barely can see launch screen of WoW but cannot click something). After I connect to monitor it can be opened even I start the game while monitor is connected and switch the main monitor to notebook (game start on notebook screen). Without monitor connection white screen comes back to notebook screen :S I am confused and need help. Thanks.