Comment 16 for bug 551721

If you are experiencing this problem, then please follow these instructions:

 * Save the output of 'fdisk -lu' to a file. In this output, take note of the start sector of the first partition (usually 63, but might also be 2048 on recent installations, or occasionally something else). If this is something other than 63, then replace 63 in the following items with your number.
 * Save the contents of the embedding area to a file (replace '/dev/sda' with your disk device if it's something else): 'dd if=/dev/sda of=sda.1 count=63'
 * Do whatever you do to make GRUB unbootable (presumably starting Windows), then boot into a recovery environment. Before you reinstall GRUB, save the new contents of the embedding area to a different file: 'dd if=/dev/sda of=sda.2 count=63'
 * Follow up to this bug with these three files (the output of 'fdisk -lu', and the embedding area before and after making GRUB unbootable).