If you want a video, TV show, DVD, or visualization to fill the entire screen when you play it, switch to full-screen mode in Windows Media Player. When the Player is in full-screen mode, you can control playback with the on-screen controls that appear at the bottom of the video screen.
For information about using the keyboard to control the Player, see Windows Media Player keyboard shortcuts. For information about different display modes, see Switch between display modes in Windows Media Player.
The playback controls might only appear for a short period of time (depending on the capabilities of your video card and the functionality of the video or DVD that you're viewing). If you're unable to see the playback controls, and haven't turned off full-screen controls, move your mouse to make them reappear.
Click the playback controls at the bottom of the screen.