I am not able to get my second 980 Ti to do anything meaningful while gaming or running benchmarks. One card does all the work, pegged at 90%+, while the other card sits idle at 0-1% usage. NVIDIA control panel indicates SLI is enabled. All low power usage settings are disabled.
 
Windows 7 Pro
i5-4670k 3.40 GHz (no OC)
16 GB RAM
EVGA SuperNOVA 750 G2 Power Supply
EVGA GeForce GTX 980 Ti FTW GAMING ACX 2.0+
EVGA GeForce GTX 980 Ti CLASSIFIED GAMING ACX 2.0+
2x 256 GB SSDs
 
Screenshot of Heaven Benchmark running with aforementioned issues: imgur.com/a/oDgKo
 
I did perform a fresh driver uninstall/install upon installation of the second card.
 
I know my PSU is not necessarily up to par (some say 850 is preferable for this setup) but I am hesitant to order another PSU if it isn't the root cause of these issues. I have never seen the system power off unexpectedly and the PSU never makes noise under load.
 
What could be the problem?

Hi,
 
Yes, Maximize 3D Performance is enabled. SLI bridge is in place. (see attached)
PCIe lanes are running at x8 (see attached).

Hey, thanks very much for your reply. I installed the latest nVidia drivers last night (378.66), and even though it made no difference initially, it seems those drivers in conjunction with all the power settings I adjusted fixed the PC *only after a restart*. So to anyone else experiencing similar issues, update to latest drivers, and then update ALL of the following power settings:
 
* On your Windows power plan (Control Panel\All Control Panel Items\Power Options\Edit Plan Settings), click 'Change advanced power settings', then select 'PCI Express' in the list. Under LInk State Power Management, set them all to Off.

* In NVIDIA Control Panel (right click on your desktop to open this), navigate to 'Manage 3D Settings' on the left. Set 'Multi-display/mixed-GPU acceleration' to 'Single display performance mode', and also set 'Power management mode' to 'Prefer maximum performance'.

* Lastly, restart your PC.

Unfortunately it would appear I spoke too soon. Tonight the issue resurfaced. I noticed WoW was again only running with 1 card pegged at 80+% while the other card sat idle at 0-1%. The same behavior occurred while running 3DMark Firestrike per MDecker's request; only the first card remained pegged the entire time. Here is the benchmark result: www.3dmark.com/3dm/18300575

Sajin
Try testing each set of sli fingers using a flexible sli bridge to see if only one set or both sets experience the same issue.
 


In the above pic you can see the flexible sli bridge only running off one set of sli fingers. Simply move the flexible sli bridge to the other set of sli fingers to test them.

Thanks, Sajin. I tried switching the flexible SLI cable to the other fingers. No effect.

Sajin
Try cleaning out your grahpics drivers with ddu & re-installing the latest drivers. Instructions on how to do that can be found under step #2. If you continue to have problems after that try doing it again except this time try driver .

Thanks for the help.
Initially when I did a clean boot to uninstall the latest version of drivers, I tried to open WoW and see how it was running. I noticed that the system was actually running with BOTH graphics cards under demand in SLI as intended; each card was running 30-60% - great. Hmm. So, in clean boot, I uninstalled MSI Afterburner and then rebooted into safe mode, as directed. I used DDU to clean drivers and restart. I reinstalled latest version of drivers along with MSI Afterburner to track the GPU usage in OSD via Riva. Problem not resolved. I repeated the steps except this time, installed 353.06. After installation of 353 and once again MSI, I fired up WoW, and initially both cards were being utilized equally, 30-50%. Without restarting the PC, I closed WoW and restarted the game, and the problem re-presented itself - GPU1 at 70-90+%, GPU2 at 1-5%.
 
In other words, I'm on 353.06 now and while it seemed to work initially for a few minutes, simply closing and re-opening the game broke it again. I'm clueless. And I'm still in 'selective startup' mode to try and eliminate any interactions with other software.
 
EDIT: Somehow in the driver re-install and uninstall process, my HTC Vive got added as an 'extended' desktop, even with the Steam client off and the VR service not running. I unplugged the power cord to my Vive and now WoW is running at proper SLI again, 60% each card..... 
 
Could this all be because of the Vive? Should I go back to the latest version of drivers? Is a total clean install necessary or can I install GeForce experience and let it do the work?

Sajin
Is everything still working with the vive unplugged? Yes, I would go back to the latest drivers. A clean install is definitely necessary. Leave geforce experience uninstalled as it's been known to cause issues.

I did follow your instructions and clean-install 378.66.
 
Unfortunately it would seem this issue is not solved. I have kept my HTC Vive unplugged from HDMI and power, so there's no way it's interacting with this. After restarting the PC, I can get both cards active in SLI while gaming for 10-15 minutes, then the second card mysteriously stops working and returns to 0%-1% usage as prior to the issue. The issue persists until the PC is restarted, after which the cycle repeats. According to MSI Afterburner the second card is reaching a max temperature of 78*C, so I don't think it's overheating.
 
I purchased a new SLI ribbon cable and tried switching it out. No effect. 
 
At this point I'm thinking either the second video card is faulty, or perhaps the second card isn't getting enough power so it's doing some sort of 'soft shutdown'. Is that plausible, as I did note I am only running 750W? I have never had an issue with power-offs or anything indicating power starvation. What should I do?