While the process SHOULD be automatic, perhaps you need to press a function key combo to get the surface to switch to external monitor? This is sometimes necessary on some laptops. IF this is the case you will see a picture of a monitor or two monitors with a slash between them above the correct function key. You would then have to press the fn and then that function key in order to get the display to switch from local display to external. It may be possible to toggle between them, AND get both to display with multiple presses. And again this is NOT always necessary, and I have no direct knowledge of how the Surface works it.