Question GPU only works in secondary pcie slot after lots of troubleshooting.

[jacobbcaudill]

Recently purchased a 7900xt from amd. I install the gpu using the same procedure I've used 10+ times at this point, and no display. Place the old gpu back into the slot, no display. Reasonably figured that it was an issue with the motherboard so I order a new one. While waiting on the new motherboard to arrive I test the card in the next full lane, and surprise, it works. Once the motherboard delivered I replace it and plug everything back in the way it was, including the gpu in the main pcie 5.0x16 slot, and no display. Again. Finally was through with it and called amd support. They recommended that the 700w evga power supply wasn't enough to supply power to the card, which was bs but it worked in other slots, but I needed one anyways so I went to an 850 watt corsair one. Install it, and no change. Neither my old card (3070ti) or the new one will work in the main slot, and with my case I can't run a card that low on the mobo for thermals. Am thinking now that my cpu is the culprit. Since, to my knowledge, the cpu controls the main lane, while the chipset on the mobo controls the rest. Since I've exhausted all my other options I'm down to the cpu. Have you all ever seen a pcie controller go bad in a cpu before? Even if I boot the pc w on board graphics neither card shows up in that slot on device manager. It's like they aren't even there. Fans spin, leds shine, but nothing in device manager.
Have tried
-booting with no drives to bios
-1 stick of ram
-other known working gpus
-mobo replacement
-new psu

My specs are
-Z690 Steel Legend motherboard
-I7 12700K cpu
-32gb ddr4 3200 trident z ram
-850 watt corsair psu
-RX 7900XT
-phanteks p300a case

I just want to know what it could be at this point other than the cpu and what could've causes it. Thanks in advance for the replies!

 

[Lutfij]

Corsair is the brand of the PSU while 850W is the advertised wattage of the unit. Please mention the model for the unit. BIOS version for your motherboard at this moment of time? As for your GPU, is it an AMD reference model or an AIB model? Without the discrete GPU, are you able to get POST/display? Clearing CMOS brings the system back to life with the discrete GPU?

 

[NerdyVixen]

Try installing the GPU in another system and see if the problem persists, if it works then it means your motherboard main PCIe x16 lane is faulty.

 

[jacobbcaudill]

Try installing the GPU in another system and see if the problem persists, if it works then it means your motherboard main PCIe x16 lane is faulty.

I've already replaced the entire motherboard

 

[NerdyVixen]

I've already replaced the entire motherboard

Model name and brand ??

 

[jacobbcaudill]

Model name and brand ??

Both were Asrock Z690 steel legend. I've even tried going into the bios and forcing gen 4 on the slot

 

[Karadjgne]

Using DP or HDMI?