This seems to be a hardware issue with a new 2.8k display I’ve installed. Even in BIOS or grub, the screen won’t stay on for longer than a minute or two (max). While it’s on, it works fine (I can sign into my Linux Mint install, which is up-to-date, do something) before it “dies” until I restart it again.
However, the 12th blink, the Display Initialization check, has always failed (while all other tests pass with green) when my laptop’s LED’s flash. I don’t really know what to do, so I’ve reseated the memory, the display connector, left my laptop on for hours, drained the battery and detached it, etc…
External displays work fine. The laptop is still running after the display goes dark (no backlight, might as well be turned off).