Compaq Evo N620C screen not working

I have a Compaq Evo Laptop Product# Dc822AV that isn't working. When you turn it on it goes to the compaq screen then the screen goes black. You can hear xp running in the background but the screen stays black. If you hook up the laptop to a external monitor everything displays and xp runs fine. Xp reconizes the laptop screen and says its enabled. I've heard that on some laptops you can set it up tp where the laptop will only work with an external monitor but I can not find this setting anywhere. If anyone has any information that might help it would be much apperciated. I found the user manual for the laptop at this link: http://h20000.www2.hp.com/bizsuppor...peId=321957&prodSeriesId=316682&lang=en&cc=us

 

Isn't there something like an FN button+screen you can press?