In this tutorial, we are going to see how to use Boot Repair to repair or re-install the GRUB boot loader under Ubuntu 11.04/10.10/10.04. Boot Repair will help you repair boot problems that may occur after installing new operating systems, or re-install GRUB when it is deleted by another OS (Multi boot).
1. Boot your Computer using a Ubuntu Live CD/USB.
2. On the first boot screen, select Try Ubuntu without installing.
3. Once Ubuntu is loaded, open the Terminal (Ctrl+Alt+T) and install Boot Repair with these commands:
sudo add-apt-repository ppa:yannubuntu/boot-repair
sudo apt-get update
sudo apt-get install -y boot-repair
4. Run now Boot Repair by opening System > Administration > Boot Repair.
5. In the next pop up message, click Advanced options. Select the OS you want to boot by default under the GRUB location tab, then select the location where you want to place GRUB into (usually sda), then click Apply to re-install the GRUB boot loader.
6. If you get this message, click Yes:
8. Wait now until the operation is finished and click OK, then reboot your system and start Ubuntu in normal mode.