That's the hard way for someone with one post.
You can also boot into a live session with the Ubuntu CD, open a terminal and issue the command:
sudo fdisk -l to see which partition is which.
If for example your Ubuntu partition on the drive is /dev/sda3, use it for grub configurations as Ubuntu updates it's kernel more often than the others, and when a kernel gets updated, so does the grub configuration file in Ubuntu to reflect the new kernel, this will save you from having to edit the file if you used the KateOS grub configuration instead of Ubuntu's when Ubuntu gets a kernel update.
Run the four commands below to reinstall grub in the MBR of the first drive set to boot in the bios, using the hard drive Ubuntu installation as root for grub configuration, remember to change the root command (second command) to reflect the proper device corresponding to the Ubuntu partition. Grub counts from 0, so /dev/sda3 is (hd0,2)
Code:
sudo grub
root (hd0,2)
setup (hd0)
quit