What the brand and model of the computer?
1. Shut the computer down.
2. When your computer is booting try pressing f1, f2, f10, f12, or DEL. One of these keys should get you into the BIOS. From there you can change the boot device order.
3. Arrange the cd rom to be the first boot device followed by your hard drive.
4. Make sure to save the settings. There will be an option in one of the menus to do that.