iMac 21.5" black screen on start up

[iMore Question]

Hi, almost every time, at least twice, when I start up my 2011 iMac from being completly off the initial start up process happens and then the screen goes completely blank, as if it's turned off, and I can still hear the machine working but can't see anything. I usually have to turn it off completely by holding down the power button and then starting it again. It usually takes at least 2 times of doing this to get it to stay on and allow me to use the machine.

It also does it some times when waking the machine from sleep. I know this isn't normal.

Does anyone have any ideas as to what this might be and what i need to do to stop it happening as I may be looking to sell the machine but can't if it's acting up like it is at present.

Cheers

 

[iEd]

I've read that there is a firmware update available for mid 2011 iMacs I would check Apple's support page for your model.


#Naked Tuesday

 

[EmceeGeek]

Sometimes the keyboard buttons to dim and brighten the screen acts up too, make sure that isn't the problem. Turn it up as bright as you can . Mine sometimes goes out and that's the problem. I guess it has a sensor in it and dims whenever the sun is shining in.


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