To do a successful installation like this, as far as I'm concerned there are 3 things that need to be taken into account:
- Select the correct disk to partition when installing Ubuntu.
- Make sure the boot loader is installed on the same disk.
- Check your system's USB boot support.
In my case, things nearly always went bad on step 3. Obviously, you need to be aware how to configure the boot loader and boot order, that's a given. But I also noticed many systems don't properly support booting off USB 3.0. By all means, try to boot a liveUSB using USB 3.0 first, or try booting from a USB 2 port for testing. My laptop nor media center (both about 2 years old) boot off USB 3. A recent desktop I put together will do so just fine.