What cable do you use for the monitor during installation ?
Do not use Dp.
Load fail safe defaults on BIOS, configure AHCI, configure display signal output from the pcie slot your adapter is installed, make your boot hdd a priority, disable AMD Cool 'n' Quiet feature if you have it.
Make sure no other monitor is connected.
Do not press any keys during the whole procedure (that means the reboots as well).
Boot in safe mode if all fails, or start from scratch (format partition etc.).
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