What to do if your Mac won`t boot from a CD or DVD?

There are cases when we need to boot our beloved Macs, not from our Macintosh HD, but from a bootable CD or DVD. Say we messed up with our Mac OS X and need to reinstall it or check our drives for errors with the system rescue CD. Here are some tips for how you can spot the causes of your problems with booting from removable media such as CDs or DVDs.

Check for hardware problems first

Yes, hardware failure is not such a rare beast. We would love to think that hardware failures do not exist in Apple's part of the Universe, but they do. In the case of booting from a CD, they mainly come from 2 sources:

●       A faulty CD or DVD. Apple's optical drives seem to be quite picky towards CDs and DVDs. Some minor scratches and stains can lead to them malfunctioning

●       A messed up CD-ROM or DVD-ROM. This is not a rare phenomenon either. A small amount of moisture or a small amount of dust (including that which comes from uncleaned disks) can lead to your SuperDrive malfunctioning. Many Mac users indicate that their slot-based CD and DVD-ROMs are quite capricious.

In any of these cases, it is a good idea to clean your CD-ROM with a cleaning CD and test whether other computers can boot from your CD or DVD.

Do not boot old systems on new Macs

If you have recently bought a new Mac and try to boot a two-year-old Mac OS X system on it, all of your efforts will be futile. A Mac can only boot the system that is not a day younger than the day when it came out of the factory.

Even if a Mac OS X boot disk arrived just days before your computer was assembled, you're out of luck. It just will not boot.

Explicitly indicate your boot medium

There are several ways of telling your Mac to boot from an optical drive if you have forgotten do this:

●      In the System Preferences section of your Mac OS X, select "Startup Disk." Select optical disk as the startup disk, and hit the restart button inside the window. During the next reboot, your Mac will start booting from the optical drive.

●      Hold the Option key when rebooting your Mac. This will force EFI (something similar to PC BIOS) to search for bootable media in the system. After it has finished, you can boot from one of the media it has located.

●      In some cases, holding the C key will make your Mac boot form a CD (depending on the firmware)

●      Older (non-Intel) Macs use Open Firmware. If your Mac is one of those, do the following when booting:

●      Press Command+Option+F+O

●      Issue one of the following commands: "boot cd:9,\System\Library\CoreServices\BootX" or "boot cd:9,\\:tbxi"

●     In some cases, the following Open Firmware commands will help: "reset-nvram", "set-defaults", "reset-al" if run in the indicated order

●      In some cases, holding Command+Option+P+R on startup allows you to boot from a CD or DVD by resetting the PRAM

Fix your Mac HDD to boot from a CD

A problem with a filesystem on your HDD may prevent a valid bootable CD from successfully booting on your Mac. The reason for that is that a bootable CD will look at your hard disk and try to find a valid system in it. A corrupt filesystem journal or even a single directory can cause it to look for such a system indefinitely without finding one.

In order to exclude this possibility, boot your Mac in the single-user mode (press Command+S at startup). In the command prompt, issue the following command without the period or quotes "fsck -fy." The filesystem utility will check your Mac HDD for filesystem errors. If, upon completion of this procedure, the utility tells you that the filesystem was modified because of errors, reboot the computer and run the same command again. Afterwards, the filesystem check utility will say that your system is okay and try to boot from the CD again.