Installed 14.04 on a non-PAE (Pentium-M), but now I can't update ("This kernel does not support a non-PAE CPU.")
When installing on a non-pae capable system using forcepae option you may still boot without this option set in Grub. Subsequent kernel updates will then fail.
To overcome this add the following line to your /etc/default/grub (source: commment #4 to bug #1307105):
GRUB_CMDLINE_LINUX_DEFAULT="quiet splash forcepae"
Then run
sudo update-grub
and reboot your system for changes to take effect.