So I ran memtest86+ on my desktop.
It didn't error!
or succeed. It just... hung, 25 minutes in.

that's probably not a good sign

I'm gonna have to start pulling parts out and get it down to a minimal hardware setup and see if it still crashes.

like, I probably could disconnect the floppy drives. those shouldn't be needed just to run memtest

even if they are clearly VITAL for day-to-day work

yanked the odd hardware like GPU and hard drives, as well as the common stuff like DVI video capture device, both floppy drives, optical drive, and serial port

I had to go find another keyboard though. my spare keyboard on hand is an AT keyboard, and while of course I have a (hand made!) AT-to-PS/2 adapter, this computer for some reason only has USB ports.

I can't understand these companies just expecting us to have obscure hardware on hand to diagnose their failures.

I normally have it plugged into a KVM but I'm bypassing that on the extreme off-chance that there's some weird interaction between the KVM and the PC

WE'VE GOT ERRORS! hitting a bunch of RAM problems around 31-39gb.

nastily that's divided between two banks. So... it's probably not just one pair of DIMMS going bad.
(and of course it's also possible it's some other problem that's causing RAM issues)

yanked half the RAM to see if it still errors

with half ram, I did two successful passes of memtest86+, no errors. time to check THE OTHER HALF (to confirm if it was just a needs-reseating/too much ram for the mobo problem)

and it passes too.
So, either my motherboard has stopped being able to support 64gb, or it was just a reseating problem. Let's stick it back in and see.

that's... probably not a good sign

I really don't like that it corrupted outside of the text window.
That shouldn't be happening if this is just a RAM problem. That's like... a GPU corruption problem.

Which is very bad because I'm currently using the CPU's on-die GPU

@manawyrm pointed out that my ram sticks weren't properly interleaved. So I'm trying memtest again with that fixed

NOPE! it ran for 3 hours, threw a ton of memory errors, then crashed in the same matrixy way.
So, back to just one pair of sticks, and I'm gonna let memtest run for a while and see if that seems stable.

OK so ran the half-ram test for nearly 8 hours with zero issues.
Now I've reattached the GPU, usb ports, serial port, floppy drives, and rust drives and optical drives (but not the m.2 ssds yet because they're boot drives) and I'm running it again, to confirm it's not a PSU problem

No issues after running for 4 hours!
I'll leave it on overnight but this seems to be functional

The only thing that's not back in is the two m.2 drives, which I doubt will make much difference.
We'll see!

It turns out the GPU wasn't in use so I can't be sure it's not still a power problem.
So I fixed that, put in the m.2, and started again

Memtest didn't complete, but for a very silly reason: I have my computer up on the desk and plugged into a different outlet for this testing, which means there's a power cable crossing the doorway.
When I left the room, moving the cable so I could go under it slid it out of the power supply and it shut off

memtest completed and now I'm going full on stress testing: playing fullscreen video, 3D games, processing a bunch of shit in the background, some VMs. you know, the usual stuff I do on an average day

I probably shouldn't try to run the VM that has 16gb of RAM allocated to it, though

Well that lasted all of 30 minutes before the system hung.
Fuck. It's not just the RAM.

So, it's probably one of motherboard, cpu, or PSU. At a stretch, it could be the GPU.

I have another spare GPU I could swap in. I have a near-identical CPU that I could swap in (it's in use, but I can temporarily borrow it).
PSU and mobo are trickier.
So, I'll have to try the easy ones first. Swap the GPU and see if windows still hard crashes like that, then the cpu, then start working on the others.

If you'd like to help me get back online (and gay cats, of course), donations would help. I'm kinda broke and not having a working computer is not going to help.

https://ko-fi.com/fooneturing

okay today's first test: I yanked out my GPU and I'm running on just the internal GPU. I'm gonna load up some videos, VMs, 3D games, and a bunch of browser tabs. See if this falls over too

I am not getting a large number of frames, and I only have one game running at the moment.

somehow I got my youtube video playing over my actual speakers but one of the games playing out the HDMI and the little speakers on the monitor. that's weird.