external monitor laptop not working

Hello,
I have a micron transport t2200 laptop,with xp, and am trying to use the
external monitor plug. It will work when I check the box, in settings, to
extend the desktop, but what I want to do is have the desktop on the external
monitor only. But as soon as I uncheck that box the screen on my external
monitor goes blank.
When I boot the computer the splash screen will come up on both monitors
but as soon as windows comes up the external monitor goes blank.
The manual for the laptop says that you can use the function key + f4 to
switch between 3 different modes of external monitor (just external, both
monitors, or just laptop)
but that does nothing.
Is there a setting I'm missing for this?