Cannot boot kernel 3.13.0-51 after dist-upgrade

[sblack55]

My system is Kodibuntu (Lubuntu with Kodi pre-installed) and it was at kernel version 3.13.0-49. A dist-upgrade has installed kernel version 3.13.0-51 and seems to have worked normally, including updates to grub that should make -51 the default boot kernel. However, it just keeps booting -49. I have tried numerous edits to /etc/default/grub, followed by sudo update-grub. /boot/grub/grub.cfg is modified, with -51 as the default menu item, but nothing changes in behavior, including the fact that the grub menu never appears. I'm guessing Kodibuntu has mods that are getting in my way, but I have no idea what they are or how to defeat them.

Help!

(Linux noob, but not a complete idiot.)