Restore Grub

From Knowledge76

HOWTO: Restore GRUB (if your MBR is messed up)

Restoring GRUB (the GRand Unified Bootloader) is quite simple in Ubuntu; instead of going through all of the "gain root access" steps, and playing with confusing shell commands, you can simply use the Ubuntu installation CD to restore it without going through all of the previous hassles.

This guide is written for System76 machines using a default partition layout. If you are not using a System76 computer or have modified you partitions previously, your process may differ slightly.

Reinstall GRUB Bootloader and MBR (Master Boot Record) for Ubuntu 9.10 and Later

Insert the Ubuntu CD and boot into the Live environment. Once it has logged in, open a terminal and type, in order:

sudo mount /dev/sda1 /mnt
sudo mount --bind /dev /mnt/dev
sudo mount --bind /proc /mnt/proc
sudo cp /etc/resolv.conf /mnt/etc/resolv.conf
sudo chroot /mnt
grub-install /dev/sda

Reinstall GRUB Bootloader and MBR (Master Boot Record) for Ubuntu 9.04 and Earlier

Download the Ubuntu Desktop Installation CD here.

Pop in the Ubuntu Desktop Install Disk and Boot to it.
Open a Terminal - Applications > Accessories > Terminal (One command per line)

sudo grub
root (hd0,3)
setup (hd0)
quit

Reboot and you're all done! Press escape when you see GRUB to boot into your Windows partition.