System dead after GPU upgrade (12900K / Strix B660 / RX 7800 XT / 750W PSU)

[PlaybyEar]

Specs:

• CPU: Intel Core i9-12900K

• Motherboard: ASUS Strix B660

• RAM: 64GB DDR4

• Storage: 1x 4TB SATA SSD, 1x 1TB NVMe SSD

• PSU: Corsair 750W Gold

• Old GPU: RTX 2060 (works fine)

• New GPU: RX 7800 XT (problem)

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Problem:
After swapping to the RX 7800 XT, the system will not power on.
No fans, no lights, no beeps, nothing.
If I reinstall the RTX 2060, the system powers up normally.

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Troubleshooting done:

• Checked and reseated all PSU cables.

• Verified PSU switch is on.

• Verified power button wiring and tried shorting pins manually.

• Confirmed power outlet works.

• Paperclip tested PSU — passes (fan spins).

• Updated BIOS to latest version.

• Cleared CMOS.

• Tried different PCIe cables for GPU (no daisy chains).

• Verified monitor and cables separately.

• Booted barebones (CPU, 1 stick RAM, GPU only) — no change.

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Additional info:

• PSU powers on fine by itself (paperclip test).

• System works fine with RTX 2060.

• System completely dead when RX 7800 XT installed.

• PSU is about two years old.

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Question:
Calculators say 750W is enough, but I’m assuming transient spikes from the 7800 XT are killing it at boot.
Would upgrading to an 850W or 1000W PSU solve this?
Or could something else be causing a full no-power state just by installing the new card?

Thanks.

[Tetras]

26 minutes ago, PlaybyEar said:

Question:
Calculators say 750W is enough, but I’m assuming transient spikes from the 7800 XT are killing it at boot.
Would upgrading to an 850W or 1000W PSU solve this?
Or could something else be causing a full no-power state just by installing the new card?

A decent 750 should be plenty enough for a 7800 XT, more likely the card is just DOA, or shorting out on something.

[podkall]

1 hour ago, PlaybyEar said:

PSU: Corsair 750W Gold

Which one?

 

It's PSU or GPU issue. But leans towards GPU if the PSU isn't something very old.

[MrSimplicity]

just RMA the card. It's clearly the problem if the system works fine putting the 2060 back in.

[PlaybyEar]

Thank you all, this does confirm my suspicions, though did little to give me the solution that I really wanted. I will RMA the card, and wait for another month or so for them to ship me a new one. 

I appreciate it.