Problems with the Radeon 4890.

Hello all. I am having a problem with my Radeon 4890 video card. First off I have 2 computers. One is an Intel E8400 w/ a Asus P5q-pro motherboard. I also have an AMD Phenom II 940 w/ a Biostar (not sure of the model) motherboard. I have 2 video cards. One is a Nvidia GEForce GT 9600 and the other is the ATI Radeon 4890. I can get the Nvidia card to work fine in either computer. The Radeon 4890 will only work with the AMD Phenom/Biostar combo. When I place the Radeon in the E8400/Asus combo there is no video output. The card receives power and the fan spins. When the card starts up I see the red lights on it light up and then go away. I know the PSU is good because it works fine with the other card and the Radeon is receiving power. I have re-seated the card many times but this does not fix the issue. I also reset my CMOS but I still do not get any video coming out of the Radeon when its in the Intel/Asus combo. I have tried HDMI and VGA and neither displays anything. Anyone have a clue as to whats going on? Thanks in advance!!

It has two 6 pin connectors. I have tried them both individually on the Nvidia card so I think everything is good. Any other ideas of what could be wrong?

individually? havent you tried plugging two of them at the same time?

I don't think this has anything to do with drivers since I can't even get to the BIOS (therefore drivers aren't being loaded by an OS yet). When I said I tried the plugs individually I meant on the 9600 (it only uses 1, I did this to prove that both of the adapters work). The card WORKS on the 650 watt OCZ PSU but does NOT WORK on the 700 watt OCZ PSU (this one is newer as well).

Yeah everything is hooked up correctly. I am just giving up and putting the cards in the computers that works