External monitor is primary and can’t see laptop monitor.

Hi,
A very frustrating problem has arisen for me. I am using a late model Samsung X50. I upgraded to Vista while it was plugged into an external monitor.
Now I don’t seem to be able to use the laptop except via an external monitor. If I unplug everything and boot up the laptop by itself I just get a blank screen on the laptop. I can only see what’s on it if I plug in an external monitor. It uses ATI Mobility Radeon X700 graphics card.
How can I regain control and be able to use laptop screen again. I have mucked around with all the display setting for extended monitors etc.