I built this system in February 2024 with an ASUS ROG STRIX Z790-H GAMING WIFI and an Intel Core i7-14700K. A few weeks ago, the PC suddenly stopped responding to the power button. The motherboard's standby RGB remains lit, but there are no fans, QLED indicators, POST activity, or other signs of startup. Clearing CMOS briefly revived it a couple of times, then it became completely unresponsive.
I returned the CPU and motherboard to the retailer. They diagnosed the original i7-14700K as faulty and replaced it, but they returned the motherboard with a note saying it had been tested successfully with their processor. After reinstalling the replacement CPU, the exact same problem remains.
I have tested the motherboard outside the case to eliminate standoff shorts, started it by shorting the power-switch pins directly, and tried two different known-working power supplies. I also tested with only the essentials, using different RAM slots, no GPU, no RAM, and no CPU. Nothing produces fan movement or QLED activity. The standby RGB is the only sign of life.
BIOS Flashback is also completely unresponsive. I formatted a USB drive as FAT32, prepared the BIOS file correctly, inserted it into the dedicated port, and pressed the Flashback button, but its LED never reacts.
The system includes an RTX 4080 SUPER, 64GB of DDR5-6000 memory, a Noctua NH-D15S cooler, and a 1000W be quiet! Pure Power 12 M PSU. Since the board behaves the same with two PSUs and even BIOS Flashback does not respond, is it effectively confirmed dead? Could cooler mounting pressure or some unusual compatibility issue cause this, or should I demand a motherboard replacement? I'm also wondering whether the retailer's testing was incomplete or simply happened to work on their bench.
1 Answer
Before escalating with the retailer, find out exactly how they tested it—especially which CPU, power supply, and test procedure they used. A board with standby lighting but no response can still be suffering from a missing PSU rail or power-control problem, so their “tested OK” result may have been genuine under their setup.
That said, you’ve already tried a second PSU, breadboarded the system, bypassed the case switch, and tested minimal configurations. A completely inactive BIOS Flashback function is particularly suspicious, since it should operate independently of the CPU, memory, and normal boot process. At this point, testing your components with a known-good motherboard would be the cleanest way to separate a board fault from a less obvious power or component issue. If the other board works, request a replacement and ask the retailer for details of their original test.
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