Yeah I have sli 970, it takes a bit of towing with it to get it working. First, verify both cards appear in control panel/device manager. Next make sure sli bridge is installed. Reinstall Nvidia drivers and reboot. Try to enable it. If it doesn't work, shut down pc and replug sli connector. You may have to reinstall drivers and replug sli connector a few times, but should work given that you have no hardware issues.