Main display

Hello,
when i loaded vista onto my laptop i used an external monitor and it was fine it worked great and i was able to make my monitor the primary display. But i gave it to a friend and when i hooked it to her Acer monitor(my was Gateway)it would only allow me to extend the display but i was not able to make it the main. I'm trying to use the laptop just a docking station (or to use it like a tower) so i need it to be able to use only the external monitor please help? I have tried everything except to reload windows with all the hardware attached that will be being used on the laptop, plus the screen on the laptop does not work unless i pinch the left top corner of the screen or give it a pinch and twist, hence the need for the external monitor.
Regards