I had this happen to me once and it drove me nuts. Try this, as it solved my problem. Some how while dragging the extended desktop to the TV, i turned loose of the mouse and it disappeared, and I could not find it. Try reaching in all directions with your mouse, and see if the screen is just out of view, on one of the edges of the screen. I know it sounds strange, but that is whagt happened to me. The screen was hiding just out of view on the top of window. I hope this helps.
