I suspect it's saying video output is the issue. You've got a 12700KF, so there's no IGP to work with. You might try the 3080 in another slot, make sure PCIe power is connected. Try another monitor/TV/HDMI cable if you have it. If you've got another GPU, that's worth testing. You can also try the GPU without PCIe power connected, see if it'll throw a error about that.
It's possible. Previous owner could of tried a firmware update and partially bricked the card, we don't know the history. You can try a DisplayPort to HDMI adapter.
With the blinking pattern. 2 seconds is VGA, 4 seconds is boot. I think you said 3 seconds in the original post. Which one is closer?
If that's correct, then it's a boot issue. There's something on the screen you can't see, leaves us at a display output issue. I'd try DisplayPort to HDMI.
Not at this point. Everything says GPU. We've got to verify that's the issue and then see what Nvidia can do to help you out if there's a remaining warranty.
None whatsoever. I haven't had any Gigabyte products personally since X58.
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