All right, this makes no sense to me, but here's what happened:
I put the most recent version of Knoppix on my flash drive. I plugged it in before powering my laptop. I hit F10 for the boot menu, which has worked normally in the past (the usb is first in the boot priority). Instead of showing me the menu, or loading anything on the flash drive, it started loading Ubuntu. It was faster than ever; I wouldn't even call it loading; it just started. I have no keyboard problems now.
Since I have idea why it's working now, I am disinclined to make any attempt to learn what's wrong. I don't want it to go awry again-- I'm even hesitant to power off. Thought that might be interesting. This hardly seems solved, but is that the thing to do with this (this probably won't go anywhere else). Unless someone else really wants to take guesses at what happened.