When you restart your computer you need to go into the boot loader and choose the drive that the cd is in. Then start up in that drive and that will start for iso file. Depending on your computer you may have to hit ESC or another key at the very beginning of your computer loading.
Make sure the CDROM is set to be the first boot device in the BIOS. With the CD in the drive, boot your computer and look for a prompt saying "Press any key to boot to CDROM".