All I did was have a tiny little peek at the BIOS settings on the new computer, and something went wonky. It was a little frightening to see the new box rendered unbootable for a little while, right at my bedtime, too.
Fortunately, doing a little reading and playing with it some, I figured out how to clear out that invalid signature stuff.
It was a relief to see the operating system come back on the screen. Whew!