The first problem was that the monitor has no drive software available. I used the command:
sudo displayconfig-gtk and selected setting: Plyg and play. This is not nessesary when Ubuntu finds right settings by default. I use a DVI to VGA cable to connect the computer.
Next I started the Screen Resolution program. First i set up the HP monitor to be turned on to full resolution.
To close the Laptop screen just set setting to "off".
Apply and close the program and then the setup was complete. Works perfect - the HP monitor is installed. Just be sure to activate the laptop monitor again before you open the lid...
