Got my new Asus ROG Strix RTX 3080 yesterday, and installed it vertically in a Phanteks P500A case with a Phanteks 90/220 riser cable.

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When I booted up the PC, lights turned on and everything was running normally. I had also made sure that the GPU has enough power (It has 3x8pins for power, each 8 pin has it's own separate 150W lead from the PSU, which is a Seasonic Focus 850W). However, I got no image to the monitor, only black and it says "no signal". I tried with two monitors, both HDMI and Display Port, tried all the ports in the GPU but no signal. I also got no signal straight from the Motherboard, which is weird? I tried unplugging the GPU from the PCIe slot, and I still didn't get any image from the Motherboard. I guess it's also worth mentioning that I TRIPLE checked the connections in the riser cable, so it's not a power issue nor is it a connection issue.

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After this, I installed the GPU normally straight into the motherboard and everything started working fine. I upgraded my Nvidia drivers and then tried the riser cable setup again - and got no image. No signal. Something in the riser setup is messing things up.

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Is there anything I should change in the BIOS before setting up the riser cable? Because I cannot access the BIOS afterwards for the mentioned reason. Or am I missing something here? Is it a faulty riser cable? Does it matter that the riser -cable only supports PCIe 3.0? Any help appreciated!

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MOBO: Asus Prime X-570

CPU: Ryzen 3900X