Raspberry Pi 3B, recently installed with the latest image. This is for an internal firewall/router so next to nothing installed: just sudo, dnsmasq and emacs. Using a Linksys USB3Gig network adapter for one side of the 'wall. Everything appears to work fine but when I booted it up yesterday after a week's absence the console came up in white on bright green. The console font appears to be slightly peculiar too, though it's hard to see, peering through a green and white fog. I rebooted, of course: same thing.
The only thing I've done (as I recall) since this worked perfectly was take the SIM card out and back it up on another machine using dd. I swear (don't they all) I've done nothing else.
How to fix this? Ideas on how it might have happened? I'm fairly new to Arch and to RPi, but I'm pretty familiar with other versions of Linux on PC hardware.