When you boot from a disc, what you're actually doing is running your computer with whatever small operating system that's installed on the CD, DVD, or BD. When you start your computer normally, you're running with the operating system installed on your hard drive, like Windows, Linux, etc.
Follow these really easy steps to boot from a disc, a process that usually takes around 5 minutes:
How to Boot From a CD, DVD, or BD Disc
Change the boot order in BIOS so the CD, DVD, or BD drive is listed first. Some computers are already configured this way but many are not.
After setting your optical drive as the first boot device in BIOS, your computer will check that drive for a bootable disc each time your computer starts. Leaving your PC configured this way shouldn't cause problems unless you plan on leaving a disc in the drive all the time.
Insert your bootable CD, DVD, or BD in your disc drive.
How do you know if a disc is bootable? The easiest way to find out if a disc is bootable is to insert it into your drive and follow the remainder of these instructions. Most operating system setup CDs and DVDs are bootable, as are many advanced diagnostic tools like the ones discussed above.
Watch for a Press any key to boot from CD or DVD... message.
When booting from a Windows setup disc, and occasionally other bootable discs as well, you may be prompted with a message to press a key to boot from the disc. For the disc boot to be successful, you'll need to do this during the few seconds that the message is on the screen.
If you do nothing, your computer will check for boot information on the next boot device in the list in BIOS (see Step 1), which will probably be your hard drive.
Most bootable discs do not prompt for a keypress and will start immediately.
Your computer should now boot from the CD, DVD, or BD disc.
What happens now depends on what the bootable disc was for. If you're booting from a Windows 10 DVD, the Windows 10 setup process will begin. If you're booting from a Slackware Live CD, the version of the Slackware Linux operating system you've included on the CD will run. A bootable AV program will start the virus scanning software. You get the idea.
Your boot should now begin.
What to Do If the Disc Won't Boot
If you tried the above steps but your computer still isn't booting from the disc properly, check out some of the tips below.
Recheck the boot order in BIOS (Step 1). Without a doubt, the number one reason a bootable disc won't boot is because BIOS is not configured to check the CD/DVD/BD drive first. It can be easy to exit BIOS without saving the changes, so be sure to watch for any confirmation prompts before exiting.
Do you have more than one optical drive? Your computer probably only allows for one of your disc drives to be booted from. Insert the bootable CD, DVD, or BD in the other drive, restart your computer, and see what happens then.
Clean the disc. If the disc is old or dirty, as many Windows Setup CDs and DVDs are by the time they're needed, clean it. A clean disc could make all the difference.
Burn a new CD/DVD/BD. If the disc is one you created yourself, like from an ISO file, then burn it again. The disc may have errors on it that re-burning could correct. We've seen this happen more than once.