Asus M2N-E freezes at WIN10 splash screen. Sometimes.

This may be a one & done question on a necro-era MB. I'm stumped.

One owner mobo, bought new by me from NewEgg circa 2006 ~ 2007.
Most components are from original build (OB) circa 2006 ~ 2007.
500W ThermalTake PS (OB).
Athlon 5600X2 (OB)
USB KB & mouse.(OB).
3GB DDR800 RAM in 4 slots (OB).
FDD (OB).
Mem card reader/USB port expansion card in a second FDD bay for front panel USB & card reader ports, all of which not often used. (OB).
NVidia GT vid card (OB).
Embedded NW and sound in use (OB).
BIOS was updated ~2009 or so to last one listed on Asus site (1701, released 2008).

It's run fine for 15 yrs. or so. Original WIN98 & early WIN7 OS's were 32 bit, so 3GB RAM (OB). Updated to 64 bit WIN7, then WIN10 on the company dime.

A few yrs. ago, it began intermittently freezing at the WIN login splash screen or, just after logging in, sometimes getting as far as rendering the desktop, then freezing. Neither KB or mouse will react. HDD indicator stays ON solid. A hard reboot always solves the freeze & it will run fine for indefinite hours afterward. I've also discovered that if I disable fast-boot and allow the RAM test at POST to count up for the entire 3GB RAM it doesn't freeze. Almost as if something has to 'warm up' or stabilize during/after long POST or hard reboot .

So far I've tried replacing:
PS,
USB KB & mouse,
Disconnect FDD, mem card reader/USB expansion card and, IDE optical drives,
Fresh WIN10 load on OB HDD,
Linux Lite, antiX and LMDE6 on different SATA HDD's.

CPU & system fans run & report RPM & temp correctly to BIOS and Linux ACPI monitors. Linux ACPI monitors also indicate system & CPU temps are normal after login.

I'd like to extend the life of this PC with a Linux distro because Micro$quish sez it's bad... it's bad...! No WIN11 for you old man.

8GB of DDR2/800 is cheap (~$20.00 & up) on fleaBay and elsewhere to make heavier Linux distros happier. That's all it would take.

I suspect whatever USB hardware on this mobo is getting flaky, but don't know how to test it specifically.

Ideas & processes to troubleshoot welcome. I know my way around a DMM & logic probe, but don't have a bench PS or 'scope. Knowledgeable advice with sound argument that it's within the n'th. degree of complete failure will be reluctantly accepted.

TYIA.

slmjim