Originally Posted by jefro
A few ideas.
Did you burn the ISO as an ISO or did you just copy the file to the disk?
Lastly is how a computer decides how to select boot media. Normally there is a bios selection. Some systems also allow a choice such as an F key when powered up to select boot order or similar named selection.
Also did you get the iso from ubuntu, mail order or did you get it from a torrent?
Like he said make sure you system is set to boot from a CD first. It could be a key like exmpale if you have a dell could be F2 or asus motherboard could be DEL key.
Make sure you set CD to boot first in your bios settings.
Second of all. Your install should be a image file. Keep in mind you can just burn the disk. You have to burn it as a image. For example be sure to use something like PowerISO.
This has a few references in it that might help burning an image.
Third of all if you are on windows download a md5checker from cnet or something like that. read on how to use your md5checker. that way you know you have a good download.
After all that reboot with cd in your drive and it should boot your ubuntu cd. Hope this helps