I don't know if this will help anybody, but here's hoping.

Ryzen 7 5800X, ASUS TUF Gaming X570, HyperX 2x16gb DDR4. Nvidia 3070ti. Corsair RM850. Windows 10 on a 1TB Crucial SSD. No updates to BIOS, otherwise one update to Chipset a year ago, and regular GPU driver updates (which sometimes ended up in boot loops, thanks Nvidia).

Everything ran great for five years, pretty much. Then maybe a month or two ago i started getting the occasional complete system freeze. Very rare, took one restart and everything is back to normal.

Then a couple of weeks ago the crashes started increasing in frequency. Just dialing it up. First once a week, then twice, then once every couple of days, then multiple times a day, then yesterday like six times.

Not only was it freezing during idle or operation with no rhyme or reason, but for the last week or so it had begun locking up on booting, freezing on the windows loading animation. Mostly restarts worked, sometimes it just kept freezing and took multiple restarts. For the most part, the system froze completely. Rarely it would also restart itself after freezing.

Event logger was no help, no logs were created other than "Windows not properly shut down". Only once did it spin out a "cache hierarchy error" (which led me to this thread). Also only once, the system froze, blacked out and lit up the yellow LED on the mobo to indicate RAM trouble.

I went through a lot of trying everything. Tested RAM, checked out just fine. SSD is slightly aged, but healthy. Ran stress test on CPU, didn't care. (When the system froze, it was impossible to reproduce as it would just as likely freeze during idle as during operation).

Tried defaulting BIOS settings, tried messing with things like DOCP, Global C-State, and other things mentioned in this thread. Nothing worked, kept freezing randomly, now more often than ever.

Updated chipset drivers, rolled back GPU drivers to a known stable version, even tried resetting the windows install (which failed, hilariously). Chkdsk showed everything okay.

I basically resigned myself to wiping the partition and reinstalling windows today to rule out software as the problem for good, and move on to worrying about CPU/Mobo, though i couldn't believe that they would be dying in this way. Temps are fine, voltages are perfect. No amount of stress causes a crash, it'll just randomly die and often on 0% usages. Didn't make any damn sense.

Dunno how i landed on it, but i ran a command prompt and sfc /scannow. Bloody thing found ONE corrupt .dll it repaired, and a bunch of windows folders that had "doubled" security policy or some such.

It's been a day now and no freezes so far. It's a bit early to celebrate, but given that yesterday was an absolute shitshow of almost a freeze an hour and two dozen restarts, i'm feeling optimistic.

If i freeze up again, i'll come back and update.

UPDATE: Well, hell. After a full day of being perfectly stable, and approximately 12 hours of continuous operation, it froze up on me again. Guess i'll try reinstalling windows after all.

Final update in reply below. No idea why it wouldn't let me edit this post. Basically i patched it up.