[Macpartners] iMac Hangs with Black Screen During Startup

[Andrew Munchbach]

Hi John--

It does sound like the POST process is fine.

I've seen instances where are fledgling hard disk can cause all sorts of
whacky boot problems.  Have you ruled out hard disk issues?  If you can't
boot to a CD, or do not wish to perform HD tests in Target Disk mode, you
can always try fsck from Single User mode.

http://support.apple.com/kb/ts1417

A drive-specific utility (like Disk Warrior) might be better suited for
finding bad sectors.  If a drive utility isn't available you can boot into
Target Disk mode and use Disk Utility on another machine to do a 7-way
zeroing of the drive.  If that works without any hangups, one can usually
assume that the HD is fine... but then we're back to the drawing board.

Good luck!
Andrew


On 7/21/11 1:17 PM, "John Canfield" <canfield at MIT.EDU> wrote:

>Hi Andrew,
>
>That article is for slightly newer iMacs than this one. But to be clear,
>I only get the flashing light and tone when attempting a firmware restore
>by holding the power button depressed. The fact that I can successfully
>start in Target Disk mode or use the Option key to bring up the startup
>disk screen implies it's not a POST problem wouldn't you think?
>
>I'm guessing I need to find some other way to reset or restore the
>firmware. If by chance, the DVD drive is not working correctly (it is
>kind of noisy), is there any other way to install the firmware
>update/restore CD?
>
>Thanks,
>
>John-Elmer
>
>
>On Jul 21, 2011, at 12:51 PM, Andrew Munchbach wrote:
>
>> Hi John--
>> 
>> The blinking light usually indicates that the Mac is not passing its
>>boot
>> test -- called POST (power-on self test).
>> 
>> You could have RAM or Firmware issues.
>> 
>> http://support.apple.com/kb/HT2538?viewlocale=en_US
>> 
>> I would look at the following article and check to see what the blinking
>> lights indicate and try testing appropriately from there.
>> 
>> Best--
>> Andrew
>> 
>> On 7/21/11 12:41 PM, "John Canfield" <canfield at MIT.EDU> wrote:
>> 
>>> 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
>> 
>