So, la, la, I installed a new Linux kernel the Debian way. Everything wonderful until I rebooted.
Quel Horreur! I get the horrible 'grub rescue' prompt. Believe me, after several hours, there is no way out of this hell.
Then, lucky me, my other Linux computers helped me make a Debian rescue live dvd (my computer refused to take a rescue usb). I used the 'rescue text', and just followed the results to reinstall grub. Now it works perfectly.