when I install my 5th gpu the 4th pci-e slot stops working, video card still shows up in gpu-z but without proper drivers and it wont display or mine. the pci-e LED lights up like normal and that slot works fine if im only using 4 cards.

is this a limitation of the older motherboard? its an x58 out of a dell/alienware XPS, dual core 1.86ghz xeon (Nehalem) if that matters
win7 x64 don't know if I should try another OS or not

not sure on exact motherboard specs I can find out if anyone thinks they can help