El Capitan 10.11.3 on iMac 5k Retina 27 Won't Wake up from Display sleep or hard drive sleep

Hello Viclr33,

Thank you for visiting Apple Support Communities.

I see that you have to restart by holding down the power button if your iMac goes to sleep. I can understand that this would be frustrating and disruptive to work.

First, to minimize the disruption and need to power off your iMac regularly, you may want to temporarily turn off the Energy Saver settings while you're working--About Energy Saver sleep and idle modes in Mac OS X. Let us know if your computer still becomes unresponsive with all Energy Saver settings turned off, as we can take a different approach with that situation.

Resetting the PRAM and unplugging peripherals are good troubleshooting steps. I'd recommend leaving external devices and hubs unplugged from your iMac while continuing to troubleshoot the issue.

Since you mentioned that you disconnected the power cable and tried to reboot, it sounds like you were resetting the SMC (system management controller) which is another good step to try.

To troubleshoot further, I recommend going through these steps from If your Mac doesn't sleep or wake when expected:

• Reset the SMC. (one more time)
  
• Reset NVRAM.
  
• Start up in Safe Mode to see if the issue is related to non-Apple startup items, login items, or kernel extensions.
  ​
• Try to isolate the issue by using another user account.

Best Regards.

My situation is even worth. I put my imac 5K into sleep on Saturday night as I would usually do in the past. i could not wake it up on Sunday morning. I think it went off , and I couldn't get it boot to the OS at all. It went off automatically after passing the 2/3 of the apply start up progress bar... I contacted the apple support, tried everything you mentioned above and couldn't get it work... I will bring to store tomorrow and see how are they going to fix it. this is frustrating! Especially for a nearly $5000 computer (chose the highest selectio When bought it) that just worked for a year...

turn off Power Nap.

Good Luck.

if you still see anything wrong to your IMAC? if so, I would recommend you to run several hardware test yourself by click Option-D when starting, and see if you come across any issues.

I brought my iMac 5k (late 2014) to the store twice, first time, they erased my hard drive and returned that to me (basically told me it's all good), but I got kennel panic several times in couple week after that. I brought into the store the second time, and they said apple care is going to replace this for me. I am now still waiting for their order to arrive, but this is really killing my confident...

Will see.

Seems like this may be a broader issue. I'm having exactly the same problem. Just forked out over $4,000 for my brand new iMac 5k (about 1 month ago). If it goes to sleep at all, it won't wake when I move the mouse or tap the keyboard. I've switched all the power settings to "Never" but of course the screen pretty much lights half the house at night - also don't want to leave it running as Apple warns that this reduces the life of the computer. If I go to the apple icon and hit "Sleep" I also can't wake it back up, needing to hold the power button down to do a full reboot.

I've done both the SMV and NVRAM a couple of times to no avail. I have no USB or external items connected to the iMac.

Pretty disappointing spending a heap of cash to have to keep rebooting to get it out of sleep mode. I'm finding it very frustrating. Not what I'd expect from an Apple product.

I'm running El Capitan as well.

It would be great to get some actual support, seeing this is happening to more than just 1 or 2 people.