I think it would help to first get a clearer picture of your setup, so how about downloading the Boot Info Script
to your Ubuntu desktop (can be the Live CD), open a terminal (Applications > Accessories > Terminal) and do:
sudo bash ~/Desktop/boot_info_script*.sh
That will create a "RESULTS.txt" file in the same directory from where the script is run, namely your desktop; please copy/paste the contents of the RESULTS.txt file to your next post, highlight the copied text, and click the pound/hash sign "#" graphic button in the forum message box so that the text will get "code" tags put around it. The results of that script will help clarify your setup and hopefully what the solution to your booting problem might be.