Another help source (if you haven't already done so). Go to your OS Help Menu. In the search field type cd.
Click on all the troubleshooting topics & Support Articles that pertain to your issue.
You can also do the same in Disk Utility. Open same up. At the bottom left of the window, click on the purple button w/the "?" in the middle. This will bring up the Help Menu.
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Try a different brand.
Top forum favorites
CDs
FUJI
TDK
Verbatim
DVDs
Maxell
Verbatim
MUST READ: The Digital FAQ
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Make sure the DVDs are not dirty, smudged and/or scratched. http://support.apple.com/kb/TS2000Mac doesn't start up from install disc
Disc Burning Quick Assist
Your drive may need cleaning. Cleaning kits can be purchased from any store that sells CD/DVDs.
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Check out the following KB Articles:
http://support.apple.com/kb/TS2288Troubleshooting a CD-ROM or DVD-ROM Disc That Does Not Appear on the Desktop
http://support.apple.com/kb/HT2801 Apple Computers: Troubleshooting the slot-loading SuperDrive
http://support.apple.com/kb/PH10866OS X Mountain Lion: If a CD or DVD doesn’t appear on the desktop
http://support.apple.com/kb/TS2000Mac doesn't start up from install disc
http://support.apple.com/kb/HT2801 Apple Portables: Troubleshooting the slot load optical disc drive
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Am I just better off getting an external hard drive?
Yup! You'll be so much happier.