It sounds like your Mac will occassionally not wake from sleep. I would use these troubleshooting steps from the article named:
OS X: When your Mac doesn't sleep or wake
The System Management Controller (SMC) is involved in managing power on your computer. Reset the SMC on your Mac if you are having difficulty sleeping or waking your computer.
Nonvolatile RAM (NVRAM)/Parameter RAM (PRAM) stores some power-related settings.Try resetting NVRAM/PRAM if you are having difficulty sleeping or waking your computer.
Some external devices can prevent your computer from sleeping. Try disconnecting items other than your Apple keyboard or mouse from the built-in USB, Thunderbolt and Firewire ports on your Mac. If this resolves the issue, try reconnecting your external devices one at a time until you find the device preventing sleep or wake. Check the documentation that came with the device, or contact the device manufacturer for more information.
Check to see if the issue still occurs when the computer is started in Safe Mode. If this resolves the issue, it could be related to a third party software item such as:
Try creating another user account, or log in as guest. See if your computer sleeps and wakes properly from the additional user account. If it does, your issue may be related to one of the following:
- a login item
- an app open in the original user account
You can disable login items from the Accounts pane of System Preferences. Try opening only one app at a time in the original user account to determine which app is preventing sleep. If you isolate the issue to a particular app or login item, check its documentation, or contact the developer of that software for more information.
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All the best,
I had these same sort of issues and tried everything. Turns out it is a known issue and Apple has a replacement program for the bad video card in many iMac models. The bad card causes grey screens, black screens, sleep issue, hard drive slowness, system spins, kernel panics, and more! Wow, all fixed at no charge at my local Apple Store!
Thank you Sterling!
Per your advice, I restarted in SafeMode, put the iMac to sleep and it woke up fine. So, like you said, that indicated to me there was likely a software conflict. So I rebooted normally and looked at my login items and found that there were two items that had the yellow triangle alert next to them (said they were missing) so I deleted them. Then I unmounted my two external hard drives and unplugged them. Then I deleted two pieces of experimental AirPlay software I had been testing (AirParrot and AirServer), then rebooted. On reboot I put the iMac to sleep, waited 30 seconds, hit the space bar and it woke up perfectly. So I set the screensaver to 1 minute, and the "turn display off" setting to 2 minutes and let it run through that routine. I hit the space bar and it woke up perfectly. I have now plugged back in all hard drives and rebooted and done those tests again and it all appears to be fixed!
hi, i also have the same problem that really annoying. i found this issue since i bought a macbook pro 15 early 2011 from my uncle few months ago. he said that the problem started since day one. i upset why didn't he report to the apple store in a first place, he said that the problem didn't bother him. so i started searching for a solution on the internet. i can't even remember how many times I've tried every single solution i found, and I'm sure i I've tried them all, but the problem still persist. but, few days ago i tried logging in with a guest user and put my macbook to sleep for a night and what happened just really surprised me, the mac woke up PERFECTLY, the thing that never happened to me since i bought my uncle's mac. and i wonder what the **** was happening on my main user login and i realised that the guest user doesn't need a password when it wakes from sleep, so i tried to back to my main user login, and disabled the password when log in then put it to sleep overnight, and voila my mac woke up perfectly! tried a few times and the screen freezes when waking up problem never happened since.
did you enable password on your system?
if so, try disabling your password and see what happen.
maybe its not a solution to everyone though, but at least you will know if your mac hardware is doing fine.