Normally, I'm pretty good at solving these problems, but damn does this one have me stumped. The card you just installed seems to be an older model, if I'm right. Double check that the card is in all the way and properly secured. Also, if your new computer was running on onboard graphics before, go into BIOS and make sure that the onboard graphics controller is disabled, and that you have the current controller set to AGP or PCI, depending on which slot you installed the graphics card on (assuming it's AGP).
You might also want to try and get the most current system drivers not only for the graphics card, but for the system itself. If your computer was originally a brand name, go to the manufacturer site, download the most updated drivers, and install them. If you built your own rig, go to the motherboard manufacturer site and download the latest Flash BIOS and board drivers.
As I said before, if your computer was a brand name, contact the computer manufacturer and purchase the necessary recovery discs that you'll need to reformat the computer.
Personally, I hate name brands. Too many hassles. I build my own rigs, so I always have everything I need to bring the system back up if something goes wrong. I know it can get costly, but hey, I save myself headaches when it comes to maintainence and repair, cause I can do the work myself.
Anyway, if all the above fails, you could try calling Microsoft directly, and see if they can help resolve the situation. And if that still doesn't work, here's what you'll need to get.
1.) 12 gauge, double-barrel, sawed off shotgun.
2.) 2 boxes of shells for said shotgun.
3.) 20 pound sledge hammer.
4.) large chopping axe.
5.) some sort of corrosive acid or nitro glycerine.
6.) LAST RESORT!!!! A rubber chicken.