Problem: cannot catch grub configuration to customize during boot time. Grub seems to skip the configuration choice.
Boot normally or, when impossible, using an installation media (choose rescue mode, read about the chroot option, you will not need sudo in this case).
sudo /boot/grub/grub.conf
Find:
default=0 timeout=0
change to:
default=0 timeout=4
or any other number of seconds suitable for your quickness.
Save and enjoy.
