Did you connect the power lead to the new card? These X800 series need a power coupler from your power supply in order to boot.
Also, ensure you have it seated snugly and reseat if unsure. You may also wish to try unplugging other cards in case you have one in the PCI slot next to the AGP slot. Most mainboard have "shared resource" AGP + PCI, so the slot next to the agp slot may share resources.
It could also simply be a bad card. If you've covered all the bases, it may just be DOA.
Overall though, your mainboard should work with that videocard with no problems. If you're getting no signal and it's refusing to even power-up.. i'd definately check proper fitment in the slot and the power-feed coupler. This also assumes you have a good, solid, 350-400W power supply or better as well.