T7820 powers self on, fails to POST

I recently purchased a used T7820 with dual xeon silver 4114 and 96GB RAM. The system runs archlinux. It's been running very well since I migrated to it sometime in February.

This morning, I did my routine weekly OS and software updates. Upon reboot, the machine failed to POST. I Tried holding the power button, and about 5-10 seconds after it powered down, it powered itself back on, again failing to post. I removed all peripherals and internal components, even down to a single processor and a single stick of ram, but the machine behaves the same way every time.

When I plug the machine in (with the side on of course) it will automatically power on. This isn't a complete surprise as I generally configure my firmware to do that. The power LED turns amber for a couple of seconds and then turns white. After 2 or 3 minutes of white, the machine will power itself back down and up again, the LED goes amber then white again, but this time it will stay powered on (seemingly indefinitely), but over about 20-30 minutes the fans will slowly ramp up to 100%.

In either of these states, I can hold the power button for 5-8 seconds and the machine powers off, but to my surprise it will power itself back on as long as it is still plugged into power. I've never had a machine power itself on after a hard power off, but perhaps that is normal for this machine.

The only new hardware I've added is a USB drive caddy, but I'm certain I've successfully rebooted since adding that device, and the machine exhibits the same behavior whether it's connected or not. I have tried using the jumper to clear the CMOS, but the machine continues to exhibit the same behavior.

This thread: https://dell.com/community/Precision-Fixed-Workstations/Precision-5820-BIOS-crash/td-p/6033407 seems like similar behavior, but I have been unable to get anything information from the serial port. Though I have not updated the BIOS recently (likely not since receiving the machine in Jan/Feb).

Does anyone have any ideas I can try to get this thing back into working order?

Thanks,

Travis