You cannot simply copy an ISO to a DVD and have it be bootable.  You must use specific software to create the DVD that is capable of expanding the ISO and creating a DVD from that image. In Windows 7, you can do this by just right-clicking the ISO and choosing "Burn Disc Image".  Other software (like CDBurnerXP and ISO Recorder) can do this to.
I have downloaded Server 2012 Standard of the Microsoft site and put the iso file on a CDROM. I have put the CD in to the CDROM and rebooted the Server, this has not triggered off the installation. How can I get the installation to work from the iso on the CD?
Installing Server 2012 Standard on to PowerEdge T420