Make sure that dvd is set as the first boot device in bios.
Another problem could be, if you burnt the iso to dvd as a file it won't boot, you need to select "create a disk image" from your burning program which extracts the iso to the dvd.
If you don't have a program that is capable of burning an iso file, free one's are available.
Free DVD ISO Burner at : http://www.minidvdsoft.com/isoburner/