Apple MC505LL/A User Manual - Page 42

 Wait a few seconds. If the computer still doesn't start up, shut it down by pressing and holding the power (®) button for about 8 to 10 seconds. Disconnect all external peripherals and try restarting by pressing the power (®) button while holding down the Option key. When your computer starts up, click the hard disk icon, and then click the right arrow. After the computer starts up, open System Preferences and click Startup Disk. Select a local Mac OS X System folder.  If that doesn't work, try using Disk Utility to repair the disk. For more information, see "Using Disk Utility" on page 49. If your MacBook Air doesn't turn on or start up Try the following suggestions in order until your computer turns on:  Make sure the power adapter is plugged into the computer and into a functioning power outlet. Be sure to use the 45W MagSafe Power Adapter that came with your MacBook Air. If the power adapter stops charging and you don't see the indicator light on the power adapter turn on when you plug in the power cord, try unplugging and replugging the power cord to reseat it.  Check whether the battery needs to be recharged. If the light on the power adapter glows amber, the battery is charging. See "Running Your MacBook Air on Battery Power" on page 34.  If the problem persists, return the computer to its factory settings by pressing the left Shift key, left Option (alt) key, left Control key, and the power (®) button simultaneously for five seconds.  Press and release the power (®) button and immediately hold down the Command (x), Option, P, and R keys simultaneously until you hear the startup sound a second time. This resets the parameter RAM (PRAM). 42 Chapter 3 Problem, Meet Solution