[SOLVED] PC won't boot after shut down unless PSU is reset

[fructosefather]

Spoiler: Specs

MB - ASRock B550M Steel Legend
CPU - Ryzen 5 3600x
CPU Fan - Arctic Freezer 34 eSports DUO
GPU - Zotac RTX 2070 Super Twin Fan
RAM - G.Skill Trident Z RGB 2x8GB
PSU - Corsair RM750 80+ Gold

I recently (this month) built a PC with the specs above, and it works flawlessly save for one bug that makes me nervous about the HW setup. When the PC is shut down and started up again, it will hang in POST with fans, lights, etc. all working (fans at full speed). The CPU and DRAM lights both activate, and the system will stay in this state until powered off. If you force shut down the PC, it will boot back into this state again. The ONLY ways to get a normal boot are:

1. Restart through Windows. This works 100% of the time, all the time. There have been no issues when I power down using this.
2. When shutting down instead of restarting, the PC will only boot if you reset the PSU switch before powering on.

When the PC boots normally after a restart or PSU reset, the CPU + DRAM lights turn on briefly before turning off, then the BOOT light turns on, followed by the VGA light. After this all lights will go out and the PC will run flawlessly. All games, etc. run fine. I've included the troubleshooting steps I have gone through to fix this:

• Updated all drivers/BIOS.
• Disabled Fast Boot in Windows (I thought this may the issue since the PC reboots fine, but doesn't start properly after shutting down. This didn't fix anything).
• Ran Memtestx86, with perfect results (no errors).
• Tested boot with only 1 stick of RAM (tried each individual stick).
• Reset BIOS/XMP etc. I am not OCing.
• Checking all HW connections and reconnecting everything.
• Taking all HW out of case and running with just components on a bench.
• Not a "troubleshooting" step per say, but the PC runs AAA games etc. fine when it boots normally, so to me this seems to rule out CPU/GPU issues.
• I do not have a MB speaker, so I haven't tested that yet. I'm not certain my MB has a speaker connection though.
• I will be reimaging by SSD with Windows soon after posting this just to be sure, but I am convinced this is a HW issue.

The issue occurs reliably and consistently regardless of any of the above troubleshooting. From what I can tell this leaves PSU and MB issues as the root cause of my troubles. Unfortunately I don't have an extra PSU to test with, but the fact that the issue only occurs during boot makes me feel like this is likely a MB issue. Of course due to the debug LEDs showing CPU and RAM, the issue may still be with one of those components but this seems unlikely.

Does anybody have any advice for me before I return my motherboard?

Thanks

 

[oldmandude1]

Possibly a faulty psu, have experienced something similar with an old psu unit.
Check that too if you can try another psu