John Probert complained that he couldn't boot from a CD or DVD.
A PC can't boot from the optical (DVD/CD) drive unless the BIOS settings tell it to do so. I can't tell you exactly how to check and change this setting on your PC, because it depends on your BIOS. But I can give you some general advice.
When you first turn on your PC, one of the first things to appear onscreen may be a message like "Press F10 for boot device." Those may not be the exact words, of course, and the key may not be F10, but you get the general idea.
If you press the button you're instructed to press, and you get the timing right (it may take a few tries to do this), you'll get a list of bootable devices from which you can select the optical drive.
What if you don't see that message? Reboot again.
Another message, which will almost certainly be there, will say something like "Press F2 for Setup." Once again, the exact words and the key to press may vary.
If you press that key and get the timing right, it will lead you to your PC's Setup screen--a program built into the BIOS and that doesn't need an operating system. Look for a submenu called Boot or Boot Options. Once there, look for an option called Boot Order (or something similar). Alter that setting to put the optical drive ahead of the hard drive.
You may also have to turn on another option that allows your PC to boot from the optical drive at all.
Once everything is set up properly, when you boot your PC, it will first check the optical drive. If it finds a disc there and the disc is bootable, it will boot from that. If the disc isn't bootable or there is no disc, it will boot from the hard drive.
One more thing: Watch the screen when you boot from an optical disc. You'll likely see a message like "Press any key to boot into...". If you don't press a key within the next few seconds, the disc will pass control to the hard drive and Windows will boot normally.