Bug#564928: the mbr needs updating

[Dennis 123321]

I had this issue this morning. It is caused by the installation of the
new grub not updating the actual mbr, and only the files in
/boot/grub/

It is a simple fix;
as root, execute something like this after you install the new package
for grub-pc. (changing the destination for your drive, this was __my
exact command__ for my computer):

     # grub-install --no-floppy --recheck --force /dev/sda3

a more generic command may look like:

     # grub-install /dev/sda

now, reboot, and it should boot perfectly.
If you install the new grub-pc and forget to update the boot sector,
you can chroot in and do it that way (thats what I did).