On Monday 28 August 2017 12:53:39 Thierry de Coulon wrote:
> I have a laptop (Thinkpad X220t) freshly reinstalled with latest openSuSE
> (I did not yet have time to check under other distributions).
>
> I installed Trinity over Gnome 3; If I boot and start Trinity (first user)
> I have nothing on the external screen (which is a beamer, 1024x768).
> Internal screen is at 1366*900.
>
> If I start a second user (under Gnome) the internal screen resizes to
> 1024x768 and I get an image on the beamer.
>
> Thierry

lol, i have a t40 XD
I don't have two screens.
You simply booted in without configuring anything?
try control center > system administration > monitor and display > resolution 
and layout
If they are erros, post them here, maybe some one else will help you.