I have Window 7 installed on my computer. Then I installed Ubuntu 12.04.
Windows 7 shown in the boot menu of Ubuntu, but can't start successfully.

So I searched to fix this problem.
I found a way, by starting the computer with Windows 7 CD and opened command line and executed the following commands.

bootrec /?
bootrec /FixMbr
bootrec /FixBoot

After this, Windows 7 started directly with succesful. But there is a new problem. Where is Ubuntu? How I can switch to it? :)

So, I started searching to fix this problem. And found a way by starting the computer with Ubuntu 12.04 Live CD and followed below steps in Terminal.

• See which partition is Ubuntu installed on:

$ sudo fdisk -l

• Mount Ubuntu partition. Pay attention "sda6" is for me.

$ sudo mount /dev/sda6 /mnt

• Install grub to mounted partition. Please notice that it's "/dev/sda", not "/dev/sda6". "sda" is the hard disk which Ubuntu installed.

$ sudo grub-install --root-directory=/mnt/ /dev/sda

• Restart the computer and run the following command:

$ sudo update-grub

Extra Tips:

If "grub-install: error: cannot find EFI directory." error message shown.

Try to specify --efi-directory:

sudo grub-install --root-directory=/mnt/ --efi-directory=/boot/efi/ /dev/sda

If "grub-install: error: failed to get canonical path of `/cow'.." error shown.

Mount EFI partition (in my example is /dev/sda3) to /mnt/boot/efi and then try:

sudo mount /dev/sda3 /mnt/boot/efi
sudo grub-install --root-directory=/mnt/ /dev/sda
 

Reference: www.webupd8.org

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