First of all, see:
, so that you can give enough feedback.
Now, i would advice to check device manager (also view hidden devices) so that you can verify the driver version of each display adapter individually; it should be the same.
A clean install of gpu drivers for both cards usually solves any problems.
1. you could try a different amd catalyst driver package,
2. you can physically reseat and/or reposition both cards (swap the pcie slots) or one at the time to eliminate the possibility of hardware failure.
3. you could try to remove one of the two cards (power off first) from your mobo and install drivers for only the first card. Then, after rebooting and checking that all goes well, you physically attach (again after powering off pc) the second gpu card, boot to windows (the drivers for the card should install automatically) and, again, check if all is well (reboot if necessary).
The above steps can be applied in combination to each other for thorough testing.
Hope it helps.
gigabyte X58A-UD3R rev.2, core i7 975 3.9ghz (stock voltage), windows 8.1 64-bit, corsair 12gb DDR3 1600mhz 7-7-7-20 RAM, sapphire HD 6990 (stock clocks), coolermaster ultimate 900w PSU.
amd catalyst 14.6 RC2 june23
09:32 AM by