Restore the boot of Ubuntu after installing Windows

We have received in recent days an interesting email from a reader who has installed Windows 7 on a PC where there was already Ubuntu. When the installation of Windows 7 is no longer accessible Ubuntu since the boot of Microsoft Windows does not recognize the Linux Distribution.
In fact we only use at startup Windows, But fortunately we can solve this problem very easily with reinstalling the Grub Boot Loader by Default on Ubuntu through the Ubuntu livecd.

After reinstall the Ubuntu startup Bootloader we can start Ubuntu or Windows, simply by selecting the Operating System that we use. Here's how ...

For reinstall Grub need to start Ubuntu (Or other distribution) from LiveCD Once we started to know the partition where Ubuntu installed to do this just start the terminal and type:

sudo fdisk -l

the result we choose the Linux partition where you installed Ubuntu for example sda3

at this point mount the partition with Ubuntu ,to do more terminal type:

sudo mount /dev/sd** /mnt

where instead of sd** insert the partition where you installed Ubuntu detected previously in our
become as sudo mount /dev/sda3 /mnt

at this point re-install Grub to do this type:

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

Be careful if we want to install Grub on another hard drive just change sda with the other hard drive or partition where we want to install Grub

At this point we can restart and now we will have our Grub of Ubuntu unless we find Windows just boot from Ubuntu type:

sudo update-grub

and reboot.