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Archived - iMac G5: Troubleshooting when your computer won't turn on

If your iMac G5 won't turn on—the display has no picture or color, and you don't hear fan or hard drive activity sounds—follow these steps to troubleshoot the issue.

This article has been archived and is no longer updated by Apple.

This article does not apply to iMac G5 (iSight) computers.

  1. Make sure that the power outlet you are plugging your computer into is working. Plug a different device (such as a working lamp) into the socket to make sure it has power, or plug your iMac G5 into another outlet.
  2. Check the power cord. Use a power cord that you know works.
  3. Check both ends of the power cord to make sure that the plug is securely inserted into both the AC outlet and back of the computer.
  4. Disconnect the keyboard, mouse, and other peripherals (such as speakers) from your computer.
  5. Remove the back cover to access the diagnostic LEDs on the main logic board (see Chapter 4 of your iMac G5 User Manual for instructions on removing the back cover).
  6. With the back cover removed, locate diagnostic LEDs 1 through 4 on the main logic board, shown above the large white arrow in the image below.

  7. Plug the power cord into your iMac G5 and into a working electrical outlet. Check to see if LED 1 is on or off.
    • If LED 1 is on, the power supply is getting power from the electrical outlet. Go to step 8.
    • If LED 1 is off, the computer's power supply should be replaced. Please schedule a service appointment with either an Apple Retail Store or an Apple Authorized Service Provider.
  8. Turn the computer on using the internal power button (press the small, metal button under the fan cover as shown below).

  9. Does the computer start up normally after pressing the internal power button?
    • If yes:
      1. Press and hold the power button until the computer turns off.
      2. Unplug the the power cord from the iMac and replace the back cover.
      3. Return the computer to the upright position.
      4. Plug the power cord back into the computer and press the power button on the back cover to turn it on.
      5. Make sure the computer starts up properly. If the computer won't start up when you press the power button on the back cover but did when you pressed the internal power button, go to step 11.
    • If no: Reset the System Management Unit (SMU) by pressing the SMU button (the small, metal button next to the internal power button, shown below).

      Note: If you're using an iMac G5 (Ambient Light Sensor) computer, your SMU was already reset when you unplugged and replugged the computer. You won't see an SMU reset button to press, and that's OK, as this action has already been done. (If you aren't sure which iMac G5 model you have, click here for help.)

  10. After resetting the SMU, press the internal power button again. Does the computer start up normally now?
    • Yes:
      1. Press and hold the power button until the computer turns off.
      2. Unplug the the power cord from the iMac and replace the back cover.
      3. Return the computer to the upright position.
      4. Plug the power cord back into the computer and press the power button on the back cover to turn it on.
      5. Make sure the computer starts up properly. If the computer won't start up when you press the power button on the back cover but did when you pressed the internal power button, go to step 11.
    • No: Go to step 12.
  11. Unplug the computer and remove the back cover. Plug the power cord back in. Press the internal power button (shown below) to start up the computer. If the computer starts up now, but not when you push the button on the back cover, please contact your local Apple Retail Store or Apple Authorized Service Provider for service.
  12. Press the internal power button (shown below) to start up the computer.


    Does LED 2 come on momentarily, or not at all?
Last Modified: Jun 12, 2013
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  • Last Modified: Jun 12, 2013
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