System will only recognize 2 out 3 GPU's

[Swimmer63]

Hoping someone can help me.  I have 3 7950's on an ASRock Z77 Extreme6, Win 7 and I can't get it to recognize the middle GPU.  Recognizes and mines the other two, just not this 3rd I just installed.
I reinstalled AMD Catalyst thinking it needed to run again to see the 3rd but that did not work.
I disabled the internal intel card thinking maybe it won't take more than 3 cards, but that did not work either. 
I am sure I am missing something embarrassingly obvious.  Can any shine light on stupidity?

[derr777]

I assume you've tried plugging your monitor into the card that doesnt work and see if that changes anything?

[Swimmer63]

Yes - I got a black screen when I restarted.  Monitor stayed asleep.  Though I should try it again as I have done a few things since.

[Chrithu]

Out of the blue, without looking up the board specifics one of the following could be true:

Board does not support more than 2 cards bios wise.

Middle PCI-E Slot is just x8 and not x16

Power cable connected to the failing card is broken

PCI-E Slot is broken

Card is broken.

Verify those step by step by trial and error.

This is more likely a failure on hardware end than on software end.

[Swimmer63]

Thanks for the advice.  Card is good as I tried it on another board.  But the rest I will need to verify.

[Chrithu]

Just looked up the board:

http://www.asrock.com/mb/Intel/Z77%20Extreme6/index.asp

The technical specs clearly state this board has only 2 PCI-E 3.0 x16 Slots. The Third one is just a mini-PCI-E aka PCIE x8 Slot, which is not capable of running video cards on.

You'd need another mainboard to make us of all three cards.

[Swimmer63]

Well that's bad news, but a time saver.  Thanks!

[Chrithu]

You're welcome

[Swimmer63]

Anyone have board they would recommend for running 3 7950's?

[Swimmer63]

Still open to suggestions as to a board with 3 full PCIe x16 slots.  I made the mistake of buying one with only 2.
Anyone..?  Anyone...?

[luckerme]

I had the same problem here.  I hope you can fix it.

[Socket54]

http://www.asus.com/Motherboards/P9X79_PRO/#specifications

The best one i came across, in specs it says it will support quad.

[GuiltySpark343]

The technical specs clearly state this board has only 2 PCI-E 3.0 x16 Slots. The Third one is just a mini-PCI-E aka PCIE x8 Slot, which is not capable of running video cards on.

I don't think this is true. The manufacturer's web page for this motherboard states:

- 2 x PCI Express 3.0 x16 slots (PCIE2/PCIE4: single at x16 (PCIE2) / x8 (PCIE4) or dual at x8/x8 mode)
- 1 x PCI Express 2.0 x16 slot (PCIE5: x4 mode)
- 1 x PCI Express 2.0 x1 slot
- 1 x mini-PCI Express slot
- 2 x PCI slots

They also state: "Supports AMD Quad CrossFireX™, CrossFireX™ and NVIDIA® Quad SLI™, SLI™"

To support quad SLI/xfire, you will need 4 slots. This would be the two PCI-E 3.0 x16 slots, the one PCI-E 2.0 x16 slot, and the one PCI-E 2.0 x1 slot. Note that for mining purposes, it doesn't matter if it is a v3.0 or v2.0 slot, and it doesn't matter if it is a x16, x8, x4, or x1. Bandwidth does not matter for GPU mining, only core clock speeds.

You could get a "riser card" to convert the PCI-E 2.0 x1 slot into a x16 slot with one of these:
http://dx.com/p/pci-e-1x-to-16x-riser-card-extension-cable-15-5cm-length-100061

Then plug your GPU into that riser card, and you'd be good to go. Similar to what this guy did:
http://home.comcast.net/~smklear/milk2.jpg

[Swimmer63]

Well my miner died last night/early this morning.  Could not figure out why but switched the 2nd and 3rd card with their PCIe slots and started it up.  All three recognized and hashing between 487-520kH/s.
I thought this board would work with three as the build was posted here in Newbie by a pro.
Now to work on board number 2.........

Oh..I wish I could get the hash rate higher (using GUIMiner) but no matter what I do, Intensity, Memory, Engine, etc. - I just can't them higher.  They are 2 Sapphire 7950 3Gb and a Gigabyte 7950 3Gb.
But for now I'm just happy I'm making money after 3 weeks of trials.

[Chrithu]

Edit: Umm yeah, sorry, didn't read last post in thread.

Congrats that it works now.

By the lower Hashrate you are getting I take it you are mining Litcoin or something. Because mining Bitcoins should be a lot faster with that setup.

[Swimmer63]

Correct.  LTC.  I have 2 small butterflies on order, but I'll eat a USB stick if they get delivered.
LTC is up to $4.  I have not done the math for a few days but I believe LTC is more profitable right now.

[Kinetic915]

Ive gotten 3 7950s on a z77 extreme 6 working solid for a few months.  Messed around with it and can't seem to get back to what I had.  Have the same problems as the OP seems like a common issue mining with this board.