For those who are having a dual (triple or quad) boot system in your computer, chances are, your bootloader might break when you update one OS to a newer version. If you are using Ubuntu (with the new Grub 2 bootloader) and you installed Windows. The Windows bootloader will erase your Grub 2 and you won’t be able to boot in your Ubuntu. As such, you will need to restore your bootloader to Grub 2.
Note: If you are still using the Grub legacy, check out this post to restore your Grub.
Requirement: Ubuntu (Karmic or Lucid) LiveCD (download it from Ubuntu.com)
Start your computer and boot into your Ubuntu LiveCD.
The first thing that we need to do is to mount your existing Ubuntu partition. If you already know your partition number (of the form sda1, sdb2 etc), you can easily mount using the following command:
sudo mount /dev/sda1 /mnt #replace sda1 with your partition number
If you are are using different partitions for the root and the home folder, make sure you record the root partition instead of the home.
Close the GParted. Open a terminal and type in the following command:
sudo mount /dev/sda1 /mnt #replace sda1 with your root partition number
sudo grub-install --root-directory=/mnt/ /dev/sdX #replace the X in sdX with your partition alphabet
You should be able to boot into your Ubuntu now.
Run the following to update your Grub 2 to include the bootloader of Windows (or other OS).