I recently got an ASUS TURBO-GTX1070-8G, but it's not pushing a signal to any of my displays. I got it secondhand from a friend, and he had the same problem with it. When I turn the PC on with the GPU installed, the fan and lights activate as well, so I know it's not bricked. It's at least somewhat capable of pushing a signal to one of my monitors, because when I have it seated in my motherboard, but not connected to power, it properly shows the error message warning me to shut down the PC and plug it into the PSU.

When I have it seated and connected to power, but have the HDMI plugged into the motherboard, the computer of course boots up with the onboard graphics, but when I load the UEFI, it doesn't register the GPU as even connected, even though its lights and fans are running. Needless to say, it doesn't show up in Device Manager in this state, either. On the other hand, when I turn on the PC and then plug the HDMI into the motherboard, nothing happens; the lights and fans spin up, but the displays never turn on.

Until I can get this GTX1070 to work, I've got two EVGA 660 Ti cards SLI'd together that work just fine.