Dell XPS 15 (L501X) with integrated Intel(R) HD graphics and NVidia GT 420M, processor Intel i5 M460.

Connecting  a external monitor with HDMI ( Dell AW 22010 or LG M2280D-PZ ) works fine with “Extend” and  “Projector Only” but does not work in “Duplicate mode” I have no image on the external monitor. See the picture. There are only two displays, the laptop and a external monitor. The external monitor is on 3.  Any idea how to solve this?