PCI video card installation issue

I am installing a Geforce 9400 GT PCI viedo card into a Dell Dimension 3000.....the problem is that I have the monitor plugged into the PCI Video Card when the computer boots and I can see it go through the boot process on the screen....it even gets to where it says Windows XP on the screen...then when it gets to where I choose my user the screen is blank....and if I unplug the monitor and plug it into the motherboard's onboard VGA then I can see everything again and choose my user and everything is fine......why cant I use the video card....in the BIOS I cant tell it to use a PCI video card....I have the selection of Onboard or Auto......I know it sees the video card because at the initial boot screen it tells me what card I have and how much ram it has...I also have the most recent Nvidia drivers installed that date January 22, 2009


What do I need to do so I can get the video card to work correctly