kernel panic-not syncing: VFS: unable to mount root fs on unknown block(0,0)

1 – Boot com liveCD ou PXE;

2 – Montar as partições /, /boot, /dev , /proc e /sys

Ex.
sda1 /boot
sda2 /

# mount /dev/sda2 /mnt
# mount /dev/sda1 /mnt/boot
# mount --bind /dev /mnt/dev
# mount --bind /proc /mnt/proc
# mount --bind /sys /mnt/sys

3 – Reinstalar e/ou atualizar o grub;

# grub-install /dev/sda
# update-grub /dev/sda

4 – Desmontar as partições;

# umount /mnt/dev
# umount /mnt/proc
# umount /mnt/sys
# umount /mnt/boot
# umount /mnt

5 – Reiniciar a máquina.

# reboot