This is how I recover Grub2 after Windows successfully overwrites my mbr. I also use this method to fix my grub config after a failed install. This usually only happens when I use /dev/sdx names over UUID's. On some motherboards simply rearranging your HDD boot order will offset the entire /dev/sdx order as well. Making your Grub entries useless, not really a big issue since you can correct the entries directly from the grub menu. Anyway lets move onwards.