Explain briefly the procedure for re-installing Grub in Linux ?

1) Download Ubuntu Installation / Live cd

2) Boot from Ubuntu Installation / Live cd – usb, burned cd etc.
3) During boot select “Try Ubuntu” , Don’t select install !
4) Mount your Linux root partition
sudo mount /dev/sda6 /mnt ( Assuming /dev/sda6 is the Linux root partition)
5) Install / reinstall grub
$ sudo grub-install –root-directory=/mnt/ /dev/sda ( where /dev/sda is your primary disk)
Installation finished. No error reported.

6) Reboot your system, remove bootable CD and we should have the boot menu ready when the system starts.

Note : There would be slight difference when using with other distros.