Fixing a Linux broken boot

If the system has been corrupted, and there is no grub menu, then boot from a live CD, open a terminal and do this:

sudo fdisk -l # find the root filesystem
sudo mount /dev/sda2 /mnt #whatever your root filesystem is
D1=dev
D2=dev/pts
D3=proc
D4=sys
sudo mount --bind /$D1 /mnt/$D1 &&
sudo mount --bind /$D2 /mnt/$D2 &&
sudo mount --bind /$D3 /mnt/$D3 &&
sudo mount --bind /$D4 /mnt/$D4

sudo chroot /mnt # You are now back in the main hard drive

cd /etc/default
cp grub grub.orig
vi grub
# change timeout from 0 to 10
# change STYLE from hidden to menu
# remove # from Terminal=console

update-grub

Reboot and now you will have a grub menu

It is possible to do an apt get update from within chroot