First step, burn into a CD the Super Grub Disk ISO
It's necessary use the command line for restoring Grub, a good option is download a automatic boot loader that can recognize our linux installation. After downloading the iso, we have to burn it into a CD: Download Super Grub Disk ISO cd-rom image
Init linux with Super Grub Disk
Insert the burned cd and select it like an option in the boot. When Super Grub Disk starts (in the boot) select GNU/Linux, now it will launch our linux distro.
Once you enter linux, execute into the command line and with root privileges:
In the Grub, we search where is it real location:
grub> find /boot/grub/stage2
With the info hdx,y displayed (for example: (hd0,4)) we are going to install Grub:
grub> root (hdx,y) grub> setup (hdx)
Exit Grub, the next time you reboot your system, it will be installed.