That will be because of teh video card not sending a signal to it though.
Go to your display settings and go to Advanced at the bottom under teh Settings tab. Does it have a load of settings (like Monitor, 3D Settings, Displays)? Or just one tab to select or something?
I ask this because you might not have the full drivers installed for the video card, and might just have the standard VGA drivers windows has installed. In which case we could give you the link to download them.
After that is set, there would be a monitor setting where you'd be able to switch between the monitor and TV, or even show both at the same time. The TV would then recieve a signal
I hope this helps