ah hah! i know what's happening!!!! And it's a common problem with external video cards (PCI Cards). This happened with a G3 and I figured out what's going on. OpenFirmware is not initializing the card. Hence no video. It's trying to use onboard video, because it doesn't consider the pci card.

I had to boot into the OS and get it setup, then reboot. After that, it would work. I just realized it!

Sorry bud, but to do this, you gotta get it into the system with onboard video. It's the only way to cure it.