Chosen Solution
From the Guides: The Mac Pro (Early 2008) logic board includes one double-wide PCI Express graphics slot and three PCI Express expansion slots, for a total of four slots. The computer comes with a graphics card installed in slot 1. You can install additional PCI Express graphics and expansion cards in the remaining three PCI Express expansion slots. Important: Graphics cards from previous Power Mac G5 models are not compatible with Mac Pro (Early 2008) models. In addition, Mac Pro (Early 2008) graphics cards are not compatible with previous models. What GPU cards are you using?
