The problem probably has to do with the difference between a PCIe x16 and a PCIe x8. Both of our MBs have a single x16 and a single x8 slot. Apparently ATI 58xx and higher cards require x16. Without this no card in the system work. So, because you have a 5970 in the second, PCIe x8, slot your system will not function.

Very disappointing.