Reinstalling MBR and grub after windows installation

• Load Ubuntu CD live on the system
• Look for the Linux partition with fdisk

fdisk -l

• Mount the Linux partition

mount /dev/sda3 /mnt

• Mount necessary partitions /proc and /dev

mount -t proc none /mnt/proc
mount -o bind /dev /mnt/dev

• Make /mnt your actual root and load bash

chroot /mnt /bin/bash

• Execute Grub and setup the root partition where the linux system is and rewrite the MBR, we can use the TAB to help us to find the partition.

grub
>root (hd0,4)
>setup (hd0)