I made a USB bootable using a program recommended by the Ubuntu website, but when ever I go to the boot menu on restart there is no option to boot from USB. I've restarted 8 times and still don't see it.
Did you select boot usb from the start up menu? Its under the F12 menu I do believe and then from the select boot sequence and make usb device first.
some machines do not support boot from USB or External hard drives. Your best option would be to create a live CD.
A live CD is the exact same as a bootable USB the only difference being a Live CD will work on any machine with a CD drive.
if you are currently using windows then your best option would be to download the Ubuntu 12.04 LTS ISO image and then download a ISO burner (there are plenty available for free try ISOBurner) once you have that downloaded burn the iso onto a blank DVDrw.
Once you have your live cd go into your BIOS settings, set your CD/DVD drive to the first boot slot and save options and exit (make sure you have the DVD in the drive at this time).
hope this helps