Try the integrated video first, then the other HD4870.
tried the integrated everything seemed fine except the onboard is not good enough to run anything, and when i put the other 4870 in, it didnt even turn on.
glad you did the processor................ now to the second part of my post. are you sure there aren't any dust balls blocking the heatsink fins under the shroud of the video card. pull video card apart, reapply thermal paste and clean the dust build up of the fins of the heat sink and reassemble. How does it work now ?
yes i cleaned it very well before putting on the paste (toothpick + toothbrush)