Later, I plugged my USB drive in, and it was recognized, but it could not be mounted. I tried all 6 USB ports I had available, with no luck. Then I tried another computer, and it worked fine. Hmmmmmmmmmmmm. Could all my USB ports be dead? Could Linux have forgotten how to use USB?
Restarting the computer solved the problem instantly. Apparently, I was a bit too over-zealous in my deleting of older kernels, and deleted the one I was using! Inserting the USB drive caused the kernel to search for the USB module, which was deleted by apt. So there was a failure. Restarting loaded the new kernel, which had all its modules intact.
So make sure you don't make the same idiot mistake I did. Although it seems like it would be a good idea to throw up a warning or dialog box when something like this happens. Apt ought to be able to notice that you are using a kernel, and not allow you to delete it. And when the kernel can't find a module, it should tell someone.
