I've checked some similar answers which suggest holding "shift" until the screen shows up, this does not work for me. I also tried restarting the system several times in a row and even powering off during the boot sequence, since grub is supposed to detect failures and show the boot screen after such an event, no luck...
I got into this mess because of changing my graphic card configuration and now the system will not even show the Ubuntu log in screen. I know the grub boot menu is intact because immediately after the system failed to boot the first time, I restarted saw the menu and decided, to try to boot normally once more... When in hind sight I would be fine if I'd only chosen to start in safe graphics mode.
I've booted the system with a 10.10 installation disk and can get to any files but grub2 now required editing /etc/default/grub and then sudo update-grub but since I'm running from CD/DVD I this isn't going to work right...
Edit: I don't yet understand the answer provided by psusi. If I say
sudo chroot /media/661ae4bd-7dde-42c9-b944-f75cebeaa1ad sudo update-grub
/usr/lib/grub/grub-mkconfig_lib: 38: cannot create /dev/null: Permission denied /usr/sbin/grub-probe: error: cannot find a device for / (is /dev mounted?).