Model A1224 / Mid 2007 and Early 2008 / 2, 2.4, or 2.66 GHz Core 2 Duo processor

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iMac cycling on and off

hi my 2008 20" i mac intel 2.66mz with 4mb ram and 500 gb hard drive refuses to run.

It carried out an automatic update a couple of weeks ago, then just kept switching itself on and off every few seconds. I have disconnected the power a lot of times for between 15 seconds and 12 hours to try ALL the different start/troubleshooting commands that I could find listed without any success so I then swapped the hard drive for a second hand one + password and the mac started using the password I got with the hard drive with previous disc owners data on it. When attempting reinstall of osx using the recovery command the install finished but my imac now has the same cycling on and off problem as before. The disc will not format or even wipe using Dban . Any advice please.

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Do you have an external boot drive or the original system installation disk? What system were you running? Was a Recovery Partition on the hard drives? Was there a Recovery partition? Whatwill it do when starting in Safe Mode (Shift key on boot).


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Does it not provide any error messages at all? Have you tried booting into single user mode to see if it will at least boot that far? If you were able to go through the OS re-install without fail on the problem dive, but then went right back to the same problem, chances are you have a bad hard drive. I would then get another drive that is new or wipeable (as in the data on the drive can be tossed), and do a clean install of OSX on that drive, then attach the problem drive with a USB to SATA adapter and try to salvage your data if you don't have a backup.

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Mike re-read the question, he changed out the drive, The problem is the update.


it has started to stop and start again after clean install of OSX!


Hi Thanks for the answer Mike your magic. No there were no error messages. I had not attempted single user mode with the replacement hard drive because previously the original would not do anything in S mode.

Your answer encouraged me to try again and it worked! startup repaired and imac booting up correctly up to now. If all goes well I will restore my files from my backup, if not I will get a new HD. Thanks again.


I guess I should check in here more often ... lol ... glad you got it working! :-)


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black will be eternally grateful.
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