I currently have an external monitor connected to my laptop via VGA. I am using Freya. My external monitor is configured to be the primary display and my laptop screen is switched off. Plank works properly and is always available on my external display. However, the wingpanel is invisible. Note, that it is there and the width required for the panel is properly reserved, but I cant see or click anything on it. When I kill the wingpanel with GNOME system monitor, it relaunches itself and appears half-assed as shown in the image. I can click on the indicators but cant see them clearly. Restarting resets the whole thing (back to invisible wingpanel). I dont have synapse installed. And slingshot always works with Super + Spacebar.