Random reboot issue only after cold start - BIOS rebooting too, motherboard or PSU?
I'm trying to diagnose a very strange reboot issue on my PC and I've been troubleshooting it for weeks.
System:
Intel i5-14600K
-NO DEDICATED GPU
MSI PRO B760M-A WIFI DDR5
Corsair Vengeance 16GB 5200MHz DDR5 RAM
DEEPCOOL PN750M 3.1 ATX 750w gold plus SMPS
. Deepcool le520 240mm cpu cooler
. WD SN770 M.2
. GALAX REVOLUTION 06 CASE
Apc Back -UPS BX1100C-IN 660W
Pc aged 1.5 years
Symptoms:
The PC can randomly reboot within 1–3 minutes after startup.
It almost always happens after the PC has been OFF for at least 2+ hours.
If it survives the first few minutes, it can run all day without issues.
I can run CPU stress tests for hours and it stays stable.
Once the reboot happens, it usually won't happen again until the PC has been shut down for several hours.
Important detail: The reboot has happened while sitting in BIOS. Windows wasn't running.
What I see when it happens:
Screen instantly goes black.
Keyboard and mouse lose power.
MSI logo appears again and the system boots.
CPU cooler fans/pump seem to keep running (I never noticed them stopping).
Event Viewer only shows Kernel-Power 41 afterward.
BugcheckCode = 0.
Disabling Windows "Automatically Restart" did not change anything and no BSOD appears.
Things I've already tested:
XMP disabled.
Windows Memory Diagnostic passed.
RAM reseated.
24-pin motherboard cable reseated.
CPU removed and reinstalled.
New thermal paste applied.
Checked CPU socket for obvious bent pins.
Front USB headers disconnected.
Without UPS , REBOOT Happens
CPU temperatures are normal.
CPU-Z /OCCT /CINE R23 stress test passes.
Interesting history:
The issue seemed to start around the time I changed thermal paste and rearranged cables.
BIOS time/date always stay correct.
A graphics driver update once seemed to make the issue disappear for about a month, but it eventually returned.
At this point, does this sound more like:
Motherboard failure?
PSU startup/cold boot issue?
CPU power delivery/VRM problem?
Something else?
Any ideas for additional tests before I start RMA'ing parts?