Booting from CD is one of those computer functions that everyone seems to assume you know how to do. Watch this video, then read this quick tip, and you too will know.
You may be able to just boot from CD without doing anything. Put a bootable CD in the drive, restart the computer, and see. If it doesn't work for you, here's what to try next:
The BIOS is the part of a PC that boots up first and figures out where the operating system is. You can usually access it by pressing a function key during boot-up. Often the proper key will be noted briefly on the screen right after you power up. If you can't figure it out at all, do a search or visit michaelstevenstech.com's Access BIOS page.
Once you're in, different BIOSs will work slightly differently, but you want to find an option for boot order.
Then you'll be presented with some gobbledygook that represents all the different parts of your machine. This is a priority list of devices from which to boot your computer. The computer checks each device in order until it finds a device that has a bootable operating system.
A fair warning: you can really mess up your computer mucking about in the BIOS, so be very, very, very, very careful what you do here.
Try to identify which item corresponds to your CD-Rom. It should say something like "CD-ROM," if you're lucky. And then find which item corresponds to your hard drive. It could be HD01, or it might have the operating system's name.
Following the on-screen instructions, move the CD-ROM up the list of priority above the hard drive. If in doubt, move the CD-ROM all the way to the top. Then save the setting.
Next time your computer boots it will check to see if a bootable CD exists in the CD-ROM drive and boot from that. If not, it will boot from the next item you have on the list--most likely the hard drive.