Only 1 out of two video cards running on rig

[ayayay]

I've got a ASRock 990FX EXTREME3 AMD Quad CrossFireX nVidia Quad SLI SATA3 USB3 Motherboard--and only one slot is reading my 7950 will I  need to replace or can this be fixed?

[Gator-hex]

Slot 0, usually the 16x one nearest the CPU, has to be populated first before you can add other cards.

Did you try a second card? Read the motherboard manual and see which it says is slot 0.

[Easy2Mine]

What are you mining?
You using Windows?

[ayayay]

I'm using the slot farthest from cpu but its the only one that works--  I have tried each slot with a total of one card at a time  using windows 7 and cg miner--- mining litcion

[Easy2Mine]

I have never mined Litecoin before, I trade it with BTC.
When I mined BTC with AMD GPU'S, Windows don't see more than 1 GPU, I have to use dummy plugs for a multi GPU setup.
It took AMD more than 1.5 years to release drivers that are capable for Windows to see more than 1 GPU.
If you know how to setup linux they work flawless with multi GPU setups.

You already have installed the latest SDK from AMD?
Read your motherboard manual and go into the BIOS.
I think the problem is there.
I had a similar  problem with an Asus M4A89GTD PRO/USB3

[Unacceptable]

I'm using a Gigbyte 990FXA-UD3 with a 7970 & 5870 for Litecoin,Running about 900khs 

You need to add a card,install vid driver,shut down,add a card,install vid driver,etc...

I'm with Easy on checking your bios settings.Or you may in fact have a defective board 

BTW,I found GUIminer Alpha is WAY easier to use for Litecoin mining 

https://litecointalk.org/index.php?topic=7722.0

Use one instance per GPU & CPU 

Here's for Nvidia:

http://www.litecoinminingmadeeasy.com/cudaminer-windows-guide.php

Good Luck!!!