6 x GPU mining rig only installs drivers for 5 I built the following rig:


5x SAPPHIRE TRI-X R9 280X 3GB GDDR5 OC (UEFI)
1x AeroCool Templarius Imperator 1150W 80 Plus Gold
1x HighPower Tech 1200w Gold Plus (HP-1200-G14C-GOLD)
1x Asrock H61 Pro BTC  Mother board
1x W.D Caviar Green 500GB SATA III HDD
1x Kingston KHX1600C9D3B1/4G
6x Powered risers 1x 16x


I Installed Windows 8.1 and plugged one GPU. It automatically installed the Radeon HD 7990 driver. Then connected the second GPU and followed the same process with the other GPUs. Everything works fine for 5 GPUs. But for the sixth one, it won't install the driver. 



I try to update the driver of the sixth one but it says that the last driver is already installed.

Regards,
(since I can't comment) I had this problem too about a month ago. Try using AMD Catalyst to install the drivers.