Computer does not recognize second GPU

edited December 2013 in Hardware support
Really impressed with the support on these threads. 
I haven't been able to find a topic on this issue yet but please redirect me if it's out there.
Any help would be greatly appreciated.
Here's what I'm trying to run:

CPU: AMD FX 4300, 3.8GHz
OS: Windows 7 64-bit
PS: 2 X (Corsair RM750) 750W for each card. 

Okay so I have got my rig up and running with one card. I downloaded the latest catalyst drivers from AMD and installed them. I got cgminer up and running and had no problems.

Next I tried booting with the second 7990 but only the first card functions (the second card's fans dont even turn on). The second card is connected to its own power supply and everything else is connected to the second power supply. 

After this I tried swapping out the cards and running that solo in the original PCI slot. However, when it boots, all the fans start pumping but there is no video output. I then put back the original card and it worked. Weird? Is this because I ran the update with the original card? 

I also know that selecting graphics cards can be done through the BIOS but i ran into issues here. I bought the same model of this mother board two days ago but it was open box and had evidence that someone was using it for mining (it powered on automatically whenever power was connected). Whenever I booted and pressed the bios setup key the screen would always go blank like it was going somewhere but would never get there. Anyways, I exchanged this for a new one today. but I ran into the exact same problem with the bios. I even updated the bios using GIGABYTE's provided program with fingers crossed and still... nothing. 

Is anybody else out there have trouble with GIGABYTE motherboard bios menu access? Can anyone please tell me how to get two cards up and running (i do not want to set up crossfire)?



  • If you have enough pcie power cables try running everything from a single power supply.  There could be power sequencing problems when one power supply is not the same as what's powering the motherboard.

    Just a guess.  If you have to run two supplies, there may be hoops you have to jump through, but I haven't tried it.


  • If each 7990 works individually, I would purchase a 1200 watt power supply and return the two 750 watt supplies. The way I think you probably have them configured (one power supply with just one 7990 and everything else on the other one) probably isn't the most ideal situation and there is likely some power issue (with one of the cards fielding power from two different sources).

  • Thanks guys!

    I have confirmed that both cards are functional on their own and that I CANNOT run each card from a separate supply. 
    Is 1200 really enough for the two cards? I read that 7990s draw 570W at max load. 

    On another note, I traded in my GIGABYTE motherboard last night for an ASUS M5A97 LE R2.0. I was really tired of not being able to access the bios after several retires and time on the phone with tech support. However, I am now having the same issue with this new motherboard:

    1) Can't access the BIOS setup menu using any of the hotkeys specified by asus. The screen just hangs blank after pressing. have to reset the comp to get out.

    2) can't install windows 7 64-bit. Windows installation starts up but the computer isnt picking up hard drives connected to is. I get prompted to load drivers so i tried loading up the ASUS CD thast came with the motherboard but I cant't find any drivers that the computer "recognizes". I ihave tried three different HDDs (all NTFS format).
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