First of all, let’s mount the related stuff;

ubuntu@ubuntu:~$ sudo mount -o ro /dev/sda1 /media/
ubuntu@ubuntu:~$ sudo mount -o bind /dev/ /media/dev/
ubuntu@ubuntu:~$ sudo mount -o bind /proc/ /media/proc/

and then chroot

ubuntu@ubuntu:~$ sudo chroot /media/

Once we are in the chroot environment, run grub

bash:~# grub

Assuming you are installing grub on your first harddisk, and your root filesystem in the first partition of your first harddisk, your journey should be something like this;

    GNU GRUB  version 0.97  (640K lower / 3072K upper memory)

 [ Minimal BASH-like line editing is supported.  For the first word, TAB
   lists possible command completions.  Anywhere else TAB lists the possible
   completions of a device/filename.]

grub> root (hd0,0)
 Filesystem type is ext2fs, partition type 0x83

grub> setup (hd0)
 Checking if "/boot/grub/stage1" exists... yes
 Checking if "/boot/grub/stage2" exists... yes
 Checking if "/boot/grub/e2fs_stage1_5" exists... yes
 Running "embed /boot/grub/e2fs_stage1_5 (hd0)"...  16 sectors are embedded.
succeeded
 Running "install /boot/grub/stage1 (hd0) (hd0)1+16 p (hd0,0)/boot/grub/stage2
/boot/grub/grub.conf"... succeeded
Done.

grub> quit

Once you’re done with that, you might want to unmount whatever you have mounted before. Don’t forget to exit from the mount directory first;

ubuntu@ubuntu:~$ cd ..
ubuntu@ubuntu:~$ sudo umount /media/proc/
ubuntu@ubuntu:~$ sudo umount /media/dev/
ubuntu@ubuntu:~$ sudo umount /media

and then reboot to see if your problem is really fixed..

The program I used was gpart, and to use it in Ubuntu (Live CD) is to add Universe repository to /etc/apt/sources.list as this;

deb http://archive.ubuntu.com/ubuntu gutsy main restricted universe

and run this commands to install it.

ubuntu@ubuntu:~$ sudo apt-get update
ubuntu@ubuntu:~$ sudo apt-get install gpart

By running the next command, gpart will search the whole disk for possible partitions and write it’s findings to the partition table:

ubuntu@ubuntu:~$ sudo gpart /dev/sda -W /dev/sda

That’s it. Just reboot and see if your system is now bootable…

p/s: Other than gpart, testdisk can also be used for partition recovery, but i’m not covering it here..