you need to change the first boot device in your bios.
when your computer starts you need to press f5 or f6 or f8 to get into the bios screen. In that screen you will fing the boot device setup screen. scroll through until you get your cd rom drive as the first boot device. Then save the changes and reboot. the computer will then boot from your cd drive.
When you have finished loading what you need, dont forget to change the bios setting back to what it was.