It seems that you've asked the same question at the Ubuntu forums as epcp - that's OK
I have been professionally engaged in computing (hardware) from 1997 to 2005 and a superuser before and after. I have never even heard of a problem like this - sometimes it goes all dark, but....
It does not make sense
I found out on BenQ's homepage
Horizontal Frequency 31 - 81 (KHz)
Vertical Frequency 56 - 76 (Hz)
Take a look in /etc/X11/xorg.conf
You should have a section like this
Identifier "Generic Monitor"
The values should be the same.
To edit you have to be root - in gnome open a terminal in X11 and
- Code: Select all
gksudo gedit xorg.conf
Before you continue open a terminal and issue xvidtune
Click cancel in the pop up that pops up and in the terminal you have the values for your laptop.
If they are very different you have a problem...
Connect the external monitor and restart X (alt+ctrl+backspace)
This is a long shot but the only thing I can think of