first you go on the center of the movie screen then right click and press setting. Then on the lower most left there's a computer screen icon- click on it. Then uncheck the enable hardware accleration. That should do it.
Next time us more detail such as what movie player you are using, and how does it not work.(ex. it won't go full screen when i click the button)
You could try double clicking the screen. <--a function that works for most movie players.