How to restore GRUB menu after Windows installation? 

  1. Read General Notes
  2. e.g. Assumed that /dev/hda1 is the location of /boot partition
  3. Read How to use Ubuntu Installation CD, to gain root user access?
  4. do

    sh-2.05b# grub
    grub> root (hd0,0)
    grub> setup (hd0)
    grub> quit