Computer has power but will not actually start.

I have a Gigabyte X58A-UD3R motherboard. All works fine. Had an nvidia geforce 8800 ultra card. Replaced the nvidia with an ati radeon hd 6870. Plugged everything back in and a few leds on the motherboard light up but it will not boot. Unplg the power to the graphics card and the systems starts to boot properly. Plug one plug into graphics card and it still tries to boot. Replaced my 500 watt power supply with a 650 watt. Same problem. I put an older nvidia fx560 card in and the system works fine. Is the card bad?
Thanks in advance.