Instructions
Run the "World of Warcraft" Launcher and press the "Play" button to open the game.
Press the "Options" button on the lower right-hand side of the log-in page. This will open a new window showing the various game options.
Click on the "Graphics" tab in the list on the left-hand side of the new window.
Find the "Display Mode" option under the "Display" heading at the top of the window and click on the drop-down menu arrow.
Select the "Fullscreen" option and double-check that all of the other options in the "Display" heading are set as you want them.
Press the "Apply" button at the bottom of this window to make the changes take effect. Press the "Okay" button to close the options menu.