Go to start and press run
type 'regedit' and enter
Go to 'HKEY_CURRENT_USER'>Softwares>Blizzards Entertainment>Warcraft>Videos
From there look for "resheight" and "resweight" and adjust the values to the proper resolution which is the actual resolution of your LCD .(*Please enter the values in decimal and not Hexadecimal)
After editing select OK and exit regedit and start the game.