HT2490: Mac Basics: Set your preferencesLearn about Mac Basics: Set your preferences
Currently Being ModeratedDec 11, 2013 12:53 PM (in response to azad25k)
Usually that is indicative of a dirty lens or DVD drive failure.
Try a DVD lens cleaning disk, a few shots of compressed air into the slot or use a fine microfiber cloth (eyeglasses cleaning cloth) wrapped around a business card gently inserted in to the slot.
If no success, take the unit to an Apple store genius bar for a free diagnosis.