If you have installed Windows after Linux, or you may have somehow lost the Grub at the startup, and are unable to load your Linux, then this article may be helpful.
Firstly, boot from your Linux or Ubuntu CD, and choose the option of trying Ubuntu without installation.
After Ubuntu gets loaded from the Live CD, you have to find out that which of the drive or partition was the one, containing your previously installed Linux. For checking out the partitions, goto the terminal ( Applications -> Accessories -> Terminal ), and write:
sudo fdisk -l
or
fdisk -l
This will show you the list of partitions you have in your system.
After you get to know the partition where your Ubuntu was installed, write the following commands. For example, if the partition is /dev/sda1, you have to write the following commands (you have to replace the sda1 from your partition name):
sudo mount /dev/sda1 /mnt
sudo mount --bind /dev /mnt/dev
sudo mount --bind /proc /mnt/proc
Now write:
sudo chroot /mnt
and then install Grub by the following command:
grub-install /dev/sda
If any errors found after entering the above line, then try this one:
grub-install --recheck /dev/sda
This is it.
Now you can reboot your system, and enjoy using your previously installed Ubuntu, after un-mounting the system by:
sudo umount /mnt/dev
sudo umount /mnt/proc
sudo umount /mnt
and simply reboot:
sudo reboot
Hope this will help you installing or recovering your Linux.