Can't SLI GTX 660s on Crosshair V Formula-Z; Don't know why

[soccercleats86]

See my system specs below.

CPU: AMD FX-8350 BE
GPUs: Nvidia GeForce GTX 660s
RAM: G.Skill Ripjaws 2x4GB 12800
PSU: EVGA G2 850W
OS: Windows 7 Ultimate
Mobo: Crosshair V Formula-Z

I've been running my GTX 660s in SLI for about a year now. First, I had a Crosshair IV, and was running them with HyperSLI. Then Nvidia released a new driver and screwed that up. So I rolled back the driver, and waited to upgrade. Finally, I got a Crosshair V Formula-Z, and the cards were running fine. Then a little while ago, I updated the Nvidia driver to 347.52. I'm not sure when exactly it happened, but a couple days after I updated the driver, I realized that SLI was not turned on. In fact, not only was it not turned on, but it wasn't an option any more. My computer can see both cards (as verified in Device Manager and in GPU-Z), it just won't let them SLI.

Things I've tried to do to fix this, all to no avail:
- Re-seated both cards, switched the cards, and booted to desktop with only one card (i.e. first with Card A, then with Card B)
- Upgraded my power supply. I had a 750; got an 850.
- Rolled back the Nvidia driver in Safe Mode using Display Driver Uninstaller
- Tried using 3 different SLI bridges
- I was going to do a system restore, then realized that the only point I could roll back to was one after I discovered this problem, so that's not an option
- Talked with Nvidia; they said (after taking a look at a system report) that the problem is that one card is running at native x16, while the other is running at native x8, even though both of them are plugged into slots that should be able to run at native x16. As of yet, I have no idea how to get the slot to run at x16. **UPDATE**: talked with Nvidia again, who confirmed that what Asus is saying (see below) is not true; PCIe 2.0 and 3.0 are both forwards and backwards compatible. Nvidia said that because I've tried everything they can think of (including rolling back to a previous driver), they think the problem is with Asus.
- Talked with ASUS; they said that my 2 GTX 660s are PCIE 3.0, and are therefore incompatible with the PCIE 2.0 slots on my motherboard. As to how I had been able to have them SLI'd for a year, they said the latest driver must have re-set the hardware. However, I look around online, and see everyone everywhere saying that 3.0 v. 2.0 should not make a difference, and that "2.0 mobos should have no problem running 3.0 GPUs" etc. etc.

Help! Please!

 

[renz496]

might as well forget that 660s SLI and get better card like 970? probably will be better for future games when some of new games can use a lot of VRAM even at 1080p. btw my 660 SLI work just fine with PCI-E 2.0. my motherboard have PCI-E 3.0 but since my CPU is from Sandy Bridge era i'm limited to PCI-E 2.0 anyway. right now i'm running with PCI-E 2.0 at x8/x8 configuration for my 660SLI. it is weird yours cannot work.

 

[soccercleats86]

I was thinking about just selling my 660s and getting a 970, as well. Otherwise, I was thinking about just switching up the motherboard (and CPU) to something that is "officially" compatible with PCIE 3.0. Either option would cost more money than I want to spend right now. You said that Sandy Bridge limits you to PCIe 2.0; is it possible that my CPU is what's causing the problem? I had a Phenom II 965 BE until early January, when I got the FX-8350.

 

[renz496]

i'm not sure about that. but PCI-E have backward compatibility. the only problem you have right now is you can't enable SLI. but as a single card can work properly on that PCI-E slots i doubt the problem is related to PCI-E.

 

[soccercleats86]

My thoughts exactly. I called Asus, and they've "escalated" my problem. We'll see what happens.