I'm working with the assumption your boot is controlled by GRUB2...
The SHIFT option was the easiest solution - if it would work.
You can edit the Grub2 settings by booting any linux LiveCD. Mount your Ubuntu partition and then edit the grub.cfg file. Find the "set timeout=0" lines and change them to "set timeout=-1" (there should be two). The -1 value will make the menu wait for your input. You don't need (or want) to run update-grub. Just save the file and boot. The menu should display, at which time you can change the settings in /etc/default/grub and change the GRUB_TIMEOUT setting.
Change the XY values to your Ubuntu partition (example: sda5
sudo mount /dev/sdXY /mnt
gksu gedit /mnt/boot/grub/grub.cfg