Why will my new video card not work for my Dell Precision 450?

I have a dell precision 450 with two gigs of RAM, 360 watt power supply. I recently purchased and new video card with 512 mb of memmory. It is a PNY Graphics Card, Geforce 6200 AGP. When I turn on my computer the monitor reads no signal and enters power save mode.|||go into the bios turn off the onboard video and your card should work!!!!