[Macpartners] iMac Hangs with Black Screen During Startup

[John Canfield]

Hello,

I can't find the solution to this problem on the regular online forums, but perhaps someone here has the answer.

It's a late, 2006, 24" iMac (Core 2 Duo) that I'm trying to completely refresh by re-partitioning/re-formatting the HDD and re-installing the operating system. Unfortunately, it now hangs with a black screen during startup. I can start it in Target Disk more with no trouble, and holding down the Option key during boot brings up the expected startup disk selection screen. But regardless of the chosen disk (or even booting from a CD), after a short while with the grey Apple screen and rotating progress indicator, it goes completely black. I can hear the disk working for a while, but it never recovers from this state.

The Apple site does mention that this particular model can exhibit such behavior, particularly when it uses Boot Camp and a Windows partition. Indeed, this machine did have such a configuration in the past (but I want it to be just OS X now). Apple suggests the following steps to fix the problem:

1) Reset the PRAM. (Cmd-Opt-P-R) - did this a few times.
2) Reset the SMC (Unplug power cord for 15 seconds) - also tried a few times.
3) Restore the firmware to factory default - I can't get this to work:

On another machine, I downloaded the correct Firmware Restoration disk image for this model (CD 1.4) and burned it onto a CD. The instructions at http://support.apple.com/kb/HT2213 say to do this:

"Turn on the computer and continue holding the Power button. The sleep LED will blink rapidly, then slowly, then rapidly (3 quick blinks, 3 slow blinks, 3 quick blinks).

On Macs that don't have a sleep LED, tones are used instead. Hold down the power button until you hear 3 long tones, then 3 short tones, then 3 long tones. 

Insert the Firmware Restoration CD while the lights are blinking or tones sounding, then release the Power button. A long tone is played once the recovery process has started."

In my case, the sleep LED starts flashing rapidly and a single long tone sounds. But then, the LED changes to steady and the machine tries to boot off its hard drive. This happens regardless of whether the Restoration CD is inserted yet. It sounds like it tries to read the CD, but instead of displaying the firmware update progress bar, it just continues as before, ultimately going to the black screen again.

I've tried booting from a Snow Leopard install DVD, and also tried putting the SL DVD on a USB drive and booting from that. The USB drive appears as expected in the startup drive screen, but when selected it just does the same thing and I get the black screen again.

There's one more fix for this problem I found on the Apple site: http://support.apple.com/downloads/iMac_MXM_Update_1_0 however, the system apparently needs to be running OS X to install this update and I can't get there from here.

Prior to starting this refresh, the machine was working fine. This is what I did to mess it up:

1) Booted the iMac into Target Disk mode and copied any useful data to another machine.
2) While still in Target Disk mode, used Disk Utility on another iMac running SL to re-partition the drive. 
3) Ran the Lion-GM installer from that other iMac to install the new OS on the Target Disk.
4) The installer seemed to run correctly, and completed to the point where I was able to set up the initial user account, etc. (still using the working iMac booting from the other's Target disk).
5) The very first time the iMac was booted from its own disk, it started up with a "patchwork" of textures and shading rather than a completely black screen, but every subsequent attempt goes to the black screen as explained at the beginning of my story.

In hindsight, I probably shouldn't have tried to re-partition and install via Target Disk mode (though that method has worked for me in the past).

Thank you for reading the lengthy details about my problem. I'd sure appreciate any clues to solving it you may have to offer.

Thanks,

John-Elmer

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