Maybe one of the 6990's is bad. Did you try the other card (alone)? Is the OC switch off (position 2)? Are both PCI-e power cables connected to the card? Try running one card alone in a different PCI-e slot.
What is the brand and model of your motherboard?
What is the brand and model of your PSU?
Tried all the above mentioned before, switch OC is off, both cables connected, tried 2 PSU together, etc.
MOBO is DFI Lanparty LT x48
PSU is CoolerMaster Silent Pro 1200W Gold
The results are the same with both cards... dont think both cards are bad... maybe but really?...