Once you've checked the integrity of your download, you should look for an option to compare the burnt disk against the original image file on your average burning application - skip MS native junk. If everything's fine, it's not the disk.
Assuming you're an windows user...
ImgBurn made wonders for me, like amazing overburns of XGD3 backups (of properly owned originals hehe) with OEM dvd writers on dirty-cheap media (nothing else could do it on W7), and it's free. Plus, it recognizes bootable image files, which's, say, important for the task.
You might also wanna try
LiLi, it makes surprisingly compatible live USB disks, out of the box. I could boot relatively
advanced/power user distributions (some known to hardly boot from live cds) on old computers without a tweak, whereas I had to refine booting options on other programs to achieve the same results.
Anyway, since we're talking about Ubuntu, things should be easier for you. What are your machine specs (motherboard model, for instance)? Consider enabling Legacy Boot on BIOS if EFI/UEFI is not working for you.