SUS Maximus XIII Hero – PC does not start, intermittent behavior

[JediNizar]

I am experiencing an issue starting my PC.

The system was working fine previously. Due to frequent travel last year, I did not use the PC often. The last time it worked normally was during my holidays in July/August.

End of November, when I tried to start the PC again, it would not boot. The RGB lights turn on, but nothing happens when I press the power button. I also tried starting the system directly via the motherboard power button, with the same result.

Observed behavior:

• No fans running

• No Q-Code LEDs active

• Only RGB lighting is on (Start and FlexKey buttons, and the BIOS Clear LED on the back of the motherboard)

Troubleshooting performed

1. I disconnected all cables and reconnected them — no change.

2. I then disconnected all components (SATA devices, GPU, etc.), leaving only:

   • RAM

   • NZXT Kraken Z73 AIO (still mounted on the CPU)

3. I also tested:

   • Without RAM

   • With the AIO disconnected from CPU_FAN / CPU_OPT / AIO_PUMP (I tried all headers)
     → No effect.

4. I suspected the PSU might only be providing 5V but not 12V.

   • PSU: be quiet! Straight Power 11 Platinum 1200W

   • I tested it using the paperclip (bridge) method, and it appeared to work.

5. After this, I paused troubleshooting for some time.

Events last Sunday

Last Sunday, I tried again and completely disassembled the PC (except the AIO). I connected only:

• PSU (ATX + CPU power cables A & B)

• RAM

• AIO Z73

Still no success.

I then attempted a BIOS update using BIOS FlashBack via USB. The button flashed blue, then faster, and eventually stopped. I assume the BIOS update was successful (the board was purchased in 2021 and had never been updated before).

After the BIOS update, the system still did not start.

A few hours later, while tidying up, I tried once more — and the system suddenly started:

• Fans were running

• Q-Code LED showed D7

I then:

• Installed the GPU → system still worked

• Mounted the motherboard back into the case (PSU and AIO still outside) → still worked

• Installed the AIO and GPU fully → still worked

• Finally mounted the PSU back into the case (requiring cable reconnection)

After reinstalling the PSU inside the case, the system would no longer start again.

Additional testing

• I suspected a loose cable connection.

• Removed the GPU → no change.

• Removed the PSU from the case without unplugging the cables → system started again.

• Disconnected CPU power cable B → system still started.

• Disconnected CPU power cable A → system started, but the Q-Code LED showed a red error code (unfortunately I do not recall which one).

• Reconnected both CPU power cables → system would not start again.

At this point, I suspected a loose connection or cable issue.

PSU replacement test

Since I was planning a new build (mini ATX) but gave up due to rising prices. I thought let's start with a PSU I ordered an ASUS ROG Loki SFX-L 1200W Titanium, which arrived today.
I tested it with the Maximus XIII Hero, but the system still does not start.

This confirms the issue is not related to the PSU or cables.

Current state

• The system worked multiple times on Sunday evening.

• Motherboard RGB lighting still turns on.

• No fans, no Q-Code activity, no boot.

I have carefully checked all motherboard pins and cannot see anything unusual that could cause a short circuit or prevent startup.

At this point, I am unsure how to proceed.
Any help would be greatly appreciated, or please let me know if the motherboard should be considered defective (bricked).

[JohnAb]

Sounds like inconsistent behaviour. Maybe changing the motherboard battery could help?