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Why won't my iMac boot?!

D

d_gomaiste

macrumors member
Original poster
Mar 18, 2016
35
0
Hey all,

My iMac (late 2012, 21.5") suddenly started having trouble booting this past week, and I'm a little worried, as I have upcoming deadlines that are pretty urgent.

In most cases, it won't even reach the white startup screen — after pressing the power button, the screen stays black, and I'm only able to tell it's "on" because my external hard drives light up, and because I can hear a very faint fan noise from the iMac itself.

I've successfully booted several times now with a simple SMC reset (unplug for 15 seconds, plug back in, wait 5 seconds, power on), but this doesn't seem to be working today.

Even if I do manage to boot up today, I'd still love to know the possible causes of this. I really don't want to have to buy a new Mac.

Any ideas or suggestions welcome. Thanks so much!!
 
How long have you waited for anything to happen after powering up before giving up? If the HD was failing, then you should at least get to the gray screen with a blinking folder and ? sign. But if it was partially failing then perhaps its kinda working and kinda not..

Can you hold down the SHIFT key during boot up to see if anything changes?

Regards
 
Raz0rEdge said:
How long have you waited for anything to happen after powering up before giving up? If the HD was failing, then you should at least get to the gray screen with a blinking folder and ? sign. But if it was partially failing then perhaps its kinda working and kinda not..

Can you hold down the SHIFT key during boot up to see if anything changes?

Regards
Click to expand...

I haven't timed it exactly, but I've definitely given it several minutes (~10) after powering on, and still nothing.

I just tried holding Shift, but to no avail, unfortunately.

When I've had success with an SMC reset, it's been pretty finicky about timing — it's as if I have to wait EXACTLY 15 seconds before plugging back in. Any more/less and it won't work. Maybe I just haven't gotten the timing right today...

Do you think a failing hard drive is likely to be the cause?

Thanks for your help!!
 
You are beyond the AppleCare warranty period, but you can at least take it to them and have them tell you what it is and how much it's going to cost. If the cost turns out to be close to a new iMac (say replacing the logicboard), then your decision is easier..
 
Did you try a PRAM reset in addition to the SMC reset?
If you get the chime continue to press keys for 2 more chimes (3 cycles)

Here's how to reset your PRAM:
  1. Shut down your machine. Yes, all the way down, not sleep or logging out.
  2. Press the power button and then press command-option-p-r. ...
  3. Hold those keys down until your Mac reboots again and you hear the startup chime.
  4. (I like to continue holding keys for another chime or 2 ... sometimes it makes a difference)
  5. Let go of the keys and let your Mac reboot normally.
 
Raz0rEdge said:
You are beyond the AppleCare warranty period, but you can at least take it to them and have them tell you what it is and how much it's going to cost. If the cost turns out to be close to a new iMac (say replacing the logicboard), then your decision is easier..
Click to expand...

Yeah, I guess that's my best bet at this point. Interestingly enough, I did some reading on Apple's discussion forums, and it looks like lots of people were experiencing a similar issue with random shut downs on the same late 2012 model:

https://discussions.apple.com/thread/6176570?start=70&tstart=0

It looks like a few users actually had their logic boards replaced, which still did not fix the issue for them. Although my problem isn't quite identical, this is still enough to make me wary of paying $800+ for a repair that might not even work.

Looks like a new Mac might be in the cards... :(
[doublepost=1502904417][/doublepost]
hfg said:
Did you try a PRAM reset in addition to the SMC reset?
If you get the chime continue to press keys for 2 more chimes (3 cycles)

Here's how to reset your PRAM:
  1. Shut down your machine. Yes, all the way down, not sleep or logging out.
  2. Press the power button and then press command-option-p-r. ...
  3. Hold those keys down until your Mac reboots again and you hear the startup chime.
  4. (I like to continue holding keys for another chime or 2 ... sometimes it makes a difference)
  5. Let go of the keys and let your Mac reboot normally.
Click to expand...

If I can get the SMC reset to work again, I will absolutely give this a try!!
 
Be sure to unplug ALL cords from the back when you next try the SMC reset (not just the power cord). Power from another connected, self-powered device, such as a USB printer, or even an ethernet network connection can occasionally invalidate an SMC reset.
 
DeltaMac said:
Be sure to unplug ALL cords from the back when you next try the SMC reset (not just the power cord). Power from another connected, self-powered device, such as a USB printer, or even an ethernet network connection can occasionally invalidate an SMC reset.
Click to expand...

Hey, thanks for the suggestion! I've actually tried this a few times, but with no success. The few times I managed to get an SMC reset to work, all peripherals (hard drives, USB mouse, iLok key, Thunderbolt audio interface, ethernet cable) were connected.
 
DeltaMac said:
You could try replacing the power supply.
Click to expand...

This seems like it's worth looking into. I've read about swapping the current one out for a "LiteOn" PSU, but a search for that brought up loads of results that are not Mac-specific. Hope I'm not making you rack your brain here, but do you happen to know how to find the appropriate unit?

Thanks again for your help!!
 
Search for "Late 2012 21.5-inch iMac power supply"
Here's one example, which also shows you Apple's part number (661-7111), Using that part number will give you other possibilities for sources.
 
Had a similar issue with my late 2012 27 iMac. It would turn off randomly and would only turn back on after being unplugged for several minutes.

Turns out it was the power supply. Apple forum has many discussions on the problem. I ordered the LiteOn PSU from eBay which solved the problem. You could also throw an SSD while you are at it. Totally worth it!
 
Hey again guys — thanks for all of the responses and suggestions, I really do appreciate it.

After reading around more and giving more thought to this subject, I think I'm just going to go ahead and buy a new Mac.

Much as I would like to try a new PSU, it seems like that pertains more to the random shutdown issue, so I'm worried that I'd be spending $100+ on something that isn't guaranteed to work for my exact problem. As for logic board replacement, that seems to be more expensive than it's worth, and it's also not guaranteed to work. I have some deadlines coming up, so it's pretty urgent that I have a 100% functional machine up and running ASAP.

That said, the only issue will be retrieving my data from my current HDD. Since it didn't fail, what would be the best way to do this? I've used Target Disk Mode in the past, but would this work with a Mac that won't boot? Should I get an enclosure for the HDD and use it that way?
 
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