you might look at the RAM
I had a 2003 HP XP laptop that kept rebooting
so old it has serial, parallel (!) and 3.5” floppy, IR, etc, i wanted to keep it alive as a relic for those old school interfaces. maybe use as an air-gapped device
but it kept rebooting. or locking up in BIOS (before “Windows” load screen bmp appeared.)
No POST beeps, by the way.
HDD checked out
swapped slots on the 2 dimms
was ok at first, then problem recurred
pulled the dimms one at a time.
ran full mem tests
One dimm was intermittently throwing errors
I just stopped using it but had decided that I could get get replacement dimms at Newegg for about $50.
might try a ham /pc fest if one’s near you to pick up some out-style dimms
The LT boots. It could be the RAM - didn’t think of that. But, it seems like it’s okay. Boot screen shows RAM okay. BIOS shows RAM okay. It’s a thought.