That is the screen saver. You right click on the desktop and from there either disable it completely or lengthen the time. I would advise against disabling it completely as you can cause damage to the monitor if you leave a static image on the screen for an extended period of time. You could cause the Taskbar to get what is known as burned in to the screen. Meaning that even when off you will always see that image on the screen causing you problems when trying to do something that doesnt have the taskbar on screen, like play a game.