Ok I give up. I need help

I have a
MSI-Z77A-GD65
Intel G1620
4GB Ram. 
2 PSU's 1 powering the mb the other powering the cards (500w on the mb, 2000w server psu on the cards)
Sapphire r9 290x cards

I'm using usb power risers. I've tried win 7,8. I'm using all Sapphire r9 290x cards with the 13.12 drivers. I can't seem to get anything to run with more than 3 cards. I've tried every pcie slot combo possible. PCIe-Gen3 is set to auto in the bios and the pcie latency settings is set to 65 (also tried 32 and 128)

What am I missing? Why can't I get past 3 cards? Any ideas? This rig is pretty stable with 3 but I can't get it to boot with 4. ideally I'm shooting for 5.