This will restore grub if you already had grub installed but lost it to a windows install or some other occurence that erased/changed your MBR so that grub no longer appears at start up or it returns an error.
Put a ubuntu live cd on your cd rom and restart and boot from cd so that you could become a live session user.........When u get into the desktop open terminal and type.....The code to be typed is highlighted so that you could easily find the codes........
This will get you a "grub>" prompt.It is the grub shell...At grub>. enter these commands
This will give you a location..whatever was returned for the find command use it in the next line
Again use the value from the find command i.e. if find returned (hd0,1) then you would enter root (hd0,1)
Next enter the command to install grub to the mbr
Finally exit the grub shell
That is it. Grub will be installed to the mbr.
When you reboot, you will have the grub menu at startup.