Dead PCIe slot?

[yerjam]

Hi everyone, new here. I've tried asking about this on other forums but I haven't got a definitive answer.

My SLI configuration has stopped working for some reason. I turned on my system and noticed my computer wasn't picking up my second video card. It doesn't show up in Afterburner, GPU-Z or Device Manager. When I go into the nVidia control panel there is no longer option to enable SLI. I've been trying to diagnose the problem and I think I may have a dead PCIe slot, but I'm not really sure, and if it is I have no idea how it happened. Here is what I've tried so far:
■Both video cards are working. I have tested them both in the top PCIe slot and they work fine.
■With a single video card in the bottom slot the system does not POST.
■However my soundcard works fine in the bottom PCIe slot.
■There is no dust or debris in any of the PCIe slots; I have cleaned them.
■The cards are definitely seated correctly. I have been swapping them around constantly to try and diagnose the problem, making extra sure to seat them right. Also, the correct power cables are attached.
■The fan on the lower video card spins, even with no power cables connected.
■I don't believe this is a driver issue; this is one of the first things I tried. I am currently on the 301.42 drivers. I have also tried the 301.24 drivers (the cards were working fine before with these drivers) but to no avail. Each time I reinstall the drivers I clean the system with Driver Sweeper and do a clean installation.
■I don't believe this is a power issue either. First, my PSU is 850W 80 Plus Gold which is more than enough to power my system, and second the system was working fine for months up until now.
■I have also reset CMOS but this hasn't done anything.

So as you can see I'm at a complete loss. The only theory I have left is that the bottom PCIe slot is dead, but this doesn't explain how my soundcard works in it alright. I thought maybe some of the pins were damaged but I can't see any damage, nothing noticeable anyway.

Here is my complete rig:
Motherboard: Asus Sabertooth P67
CPU: Intel i7 2600k
RAM: 4x4GB Corsair Vengeance LP
Video cards: 2x Zotac GTX560Ti "448" Editions
Soundcard: Asus Xonar DGX 5.1 PCIe
PSU: OCZ ZX 850W 80 Plus Gold

Any help is appreciated.

 

[InvalidError]

So as you can see I'm at a complete loss. The only theory I have left is that the bottom PCIe slot is dead, but this doesn't explain how my soundcard works in it alright.

The sound card only requires PCIe x1 to work. If the fault is on lanes 2-8, it may affect GPUs but not sound or other x1 cards.

 

[yerjam]

The sound card only requires PCIe x1 to work. If the fault is on lanes 2-8, it may affect GPUs but not sound or other x1 cards.

Ok, I understand. So would you say I should RMA the motherboard? Is there anything else I should try first?

 

[InvalidError]

First thing would be to check whether or not the single card in the working x16 slot operates at x16. If it does operate as x16, at least you know the CPU's PCIe lanes are working and the problem definitely is on the motherboard. If you only get x8, the problem might be the PCIe multiplexing chips on the motherboard or the CPU.

 

[yerjam]

I can confirm the working PCIe slot operates at x16. So looks like the motherboard is the issue then. Thanks for your help.

Anyone much experience with Asus motherboards for RMA? Never had to RMA something before, just wondering how long it should take, etc.?

 

[yerjam]

Replaced my motherboard and now I'm running SLI with no issues. Thanks for the help InvalidError.

 

[yerjam]

Best answer selected by yerjam.