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Why is my Mac not turning on after power outage?

After a power outage my Mac will not turn on. The fan is running but the screen will not turn on, it seems to be making a buzzing sound.

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What are the last four digits of your computers serial number. That will help us to properly identify your hardware.


I tried resetting the PRAM and the power came on but I'm not getting a chime and nothing on the screen. The serial number is W8549MHDTAR


My computer not turning on at all after a power outage , no sound no nothing, I unplowed it waited a bit and plugged it back a few times , but nothing happens!! Any help appreciated


I did both of these PRAM&SMC resets and it didn't work. I get the Chimes and then the Apple symbol and the status bar and about halfway through the status I get a " panic cpu1 caller launch exited" message with a whole bunch of other information. Then it tries to restart itself. Also after I did the SMC reset the fans started blowing louder than I've ever heard them before. Anything else I can try before I have to take it in to be serviced?


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Samantha, start with this:"

Reset your computer’s PRAM (Parameter RAM):

If y -- our iMac is on, turn it off by holding the power button until the unit powers off. You should hear the fans go quiet.

-- While the computer is off, with your left hand, hold down the Apple key, the Option key next to it, and the letter “R” key on the keyboard. When you have these keys all pressed down, push the power button with your right hand and then quickly move that hand to hold down the letter “P” on the keyboard. Keep these four keys pressed while the computer starts up.

-- Make sure you hold down the four keys (P - R - Apple - Option) while the computer is starting up. When you hear the computer’s start up chime for the second time, you can let go of the keys on the keyboard.

-- If you didn’t hear at least two startup chimes, go to the top of this section and begin again. It’s important that you hear two startup chimes when performing this procedure.

This indicates that you have successfully reset the computer’s PRAM (Parameter RAM).

Reset the SMC (Formerly SMU).

-- Turn off the computer by choosing Shut Down from the Apple menu, or by holding the power button until the computer turns off.

-- Unplug all cables from the computer, including the power cord.

-- Wait 15 seconds.

-- Plug in the power cord while simultaneously pressing and holding the power button on the back of the computer.

-- Let go of the power button.

-- Press the power button once more to start up your iMac.

Diagnostic LEDs

The iMac (20-inch Late 2006) has three built-in diagnostic LEDs and a front power-on/sleep LED on the main logic board that can help you to troubleshoot the computer.

To Access the Diagnostic LEDs:

1. Follow the take apart instructions to remove the RAM access door, front bezel, and lower EMI shield.

2. Locate the SO-DIMM slot and LVDS video connector. The three diagnostic LEDs 1, 2, and 3 are located below the battery and to the right of the memory slot. Note that the LEDs are marked 1, 2, 3 as show below. An additional front bezel LED is located in an opening at the center of the right speaker.

LED #1

• Indicates that the trickle voltage from the power supply has been detected by the main logic board. This LED will remain ON whenever the iMac is connected to a working AC power source. The LED will remain on even when the computer has been shut down or put to sleep.

The LED will turn off only if the AC power source is disconnected or the power supply is faulty.

LED #2

• Indicates that the main logic board has detected proper power from the power supply when the computer is turned on. This LED will be ON when the computer is turned on and the power supply is working correctly.

LED #3

• Indicates that the computer and the LCD display are communicating. This LED will be ON when the computer is turned on and video signal is being generated.

Front LED • Indicates that the computer has power but no video signal (e.g., the computer is starting up or the display has entered Sleep mode, turning off the video signal). This LED will pulse when the entire system has entered Energy Saver mode.

Let us know what you find. The buzzing could be coming from your power supply or your inverter. Try an external monitor and see if that shows you anything.

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Thanks for the detailed explanation of the internal LED's. It filled in the gaps in what I have learned piecemeal from iFixit posts generally.


THANK YOU!! Did the RESET SMU and it fired back up! Saved me lots of time and effort, god bless you.


My Imac hasn't been turning on after a power surge from a blow-dryer. However the imac was plugged into a surge bar. I have read numerous reviews of this happening to people and someone said they talked to a worker at an apple store and he said that your computer goes into a locked state anywhere from 24-72 hours after. I just want to know if I should leave my computer unplugged or plugged in while I wait for it to decide when it wants to turn itself back on? Does this matter?! Any help would be appreciated :)


@grimaldi, turn off and do the power management reset as well. You won't hurt a thing by turning it off and it'll probably be worse to leave it on anyway....(if you haven't found a fix yet)


Absolutely @grimaldi. Did this ever work for ya? Just curious...I know it's been over a year lol.


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I haven't read all the replies but you need to do an “SMU reset" the way to do this varies on every machine so Google that with your machine info and you should be good to go. Also doanother pram reset if you haven't (after the SMU) and then make sure it's all charged up before shutting down again (if it's a laptop). Hope this helps. It should. I've had this happen. Its pretty common. I'm sure most peeps here have had this happen at least once. Cheers

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Samantha будет вечно благодарен.
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