I'm trying to boot Ubuntu on an old PC with Windows XP. I've changed the boot order in BIOS several times and have even purchased an external optical drive because I assumed it couldn't read the disk. Still, no luck.
What am I missing?
Have you tried the latest version of Ubuntu? Sometimes you may have better luck with an older version. Also, does your BIOS allow for a USB boot? You can download UNetBootin to push a Ubuntu ISO to create a bootable thumb drive.
Secondly, are you sure you burned a good copy of Ubuntu? Could it possibly be that the ISO you burned was corrupted? It's usually a good idea to check the ISO against the MD5 checksum that's provided.
Finally, could it have been your disc drive? Have you tried burning a new CD with the new external drive?