Comment # 5 on bug 1208645 from Ra���l Osuna

Well, only one of them is on.
Just to be sure, I executed "xrand --auto" again.
One of the external screen is on, and the laptop screen mirrors it (or the
other way around). The other two screens stay off.
Is that what xrandr is showing? Do I only need to tell xrandr which screens I
want and the position? I think I can try that (I don't remember the syntax
right now, but I guess I'll figure it out).

If xrandr says that all 3 of them should be on, there's a problem then.