Teste isso:
Inicie o computador com um live-dvd / usb.
Abra um terminal.
Execute:
sudo -i
apt-get update
apt-get install lvm2 cryptsetup
modprobe dm-crypt
cryptsetup luksOpen /dev/sda2 crypt1
*##Write the passphrase##*
vgscan --mknodes
*##Save the volume name##*
mount /dev/<volume-name>/root /mnt
mount /dev/sda1 /mnt/boot
mount --bind /dev /mnt/dev
mount --bind /dev/pts /mnt/dev/pts
mount --bind /proc /mnt/proc
mount --bind /sys /mnt/sys
cp /etc/resolv.conf /mnt/etc/resolv.conf
chroot /mnt
apt-get update
apt-get install --reinstall 'linux-image-3.8*'
update-grub
apt-get clean
umount /mnt
reboot