Souns like the new vid card may not have the right drivers, or rather XP Pro doesn't have the right drivers for it.
Go back and use the one that worked until you get the system up and running. Then change the video card and follow the install procedures. That usually involves removing the old one in Device Manager along with the drivers, shutting down, switching cards and rebooting. It should then go into the "found new hardware routine."
Assume you are using an AGP card. There are some that do not like to share IRQs with anything. Usually PCI slot 1 is shared with the AGP slot (intended for a PCI video card, so it is an either or arrangement.) If you have something else in PCI #1, try moving it to another slot.