Comment # 16 on bug 1047307 from Stefan Dirsch

(In reply to Simon Herrmann from comment #13)
> I am using Gnome, if that's what you mean by 'which desktop'. The monitor is
> BENQ 2400 Eco (FullHD).

Ok. GNOME should definitely have a tool for the display/screen setup. Question
is still open, whether "xrandr --auto" did help to enable the external monitor.

(In reply to Simon Herrmann from comment #14)
> > Apart from this it's an Intel/NVIDIA combo. Always kind of problematic.
> > Things get easier when disabling one of the devices in BIOS/Firmware - if
> > possible.
> 
> I don't see an option in the BIOS for choosing or disabling a graphics
> adapter.

Ok. Meanwhile I believe I can rule out an issue with the Intel/NVIDIA combo.
Seems Intel is enabled and connected to the external outputs. NVIDIA probably
is only used for better rendering performance (optional).

(In reply to Simon Herrmann from comment #15)
> > BTW, most likely the desktop was confused by the strange monitor layout
> > (internal display having a different and even bigger resolution than the
> > external one), made some unlucky/wrong assumptions and failed completely in
> > the end.
> 
> Actually I chose this monitor layout, because the one before was incorrect.
> Could that really prevent the monitor from showing something? I hope not...
> (as it works on Ubuntu just fine)

Can't say. Please try 'xrandr --auto' as outlined before and above.(In reply to 

Simon Herrmann from comment #12)
> > Picture of the setup
> 
> Thank you for the drawing, that is actually my setup, because my external
> monitor is left of my Laptop screen. But the external monitor is much bigger
> than the internal display. Gnome does not seem to know about differently
> dense panel resolution ;-)

Oh. You did this by intention. Wow!