Have you tested installing them one by one and see when it fails? Did you try testing the two newer cards separately?
They are both the same, right? Same manufacturer and so on.
Also, check if you have crossfire/SLI enabled, if it is, disable it.
All four are the same. Well apart from the original ones are the "OC" version and the new two are regular version. All micron memory, same manufacturer and same model (apart from the OC).
Is the SLI/Crossfire an option in the UEFI that i need to disable (cant remember seeing any option when i changed to gen2 pcie) or am i able to disable it in windows?