HD 4670 in a Dell Optiplex 320...No Video

Hello,

I just purchased an HD 4670 graphics card and attempted to install it in my kid's computer (Dell Optiplex 320)...but I cannot get an image to come up on the monitor to save my life! After initially not getting an image, I did some research and found my PSU was underpowered...so I bought a new one (G-lite 460W PSU). Still nothing. I tested the card to make sure it's working and it is (tested it in my desktop). I cannot figure out why the graphics card is not working! If anyone has any ideas, I would love to hear them.

Intel P4 3.2GHz processor
4GB Ram
ACPI\PNP0C02\17 motherboard

If there's additional information needed to help me solve this problem, please let me know. Thanks in advance!!!