There might be an issue that some iMac users experience where subsequent to being in rest for a timeframe, their frameworks will no more react to key presses or other info, and despite the fact that squeezing the force catch ought to comparatively wake the framework, doing this comparably has no impact. With this issue, influenced frameworks require either the force catch be squeezed and held for ~10 seconds, or the force line is pulled to close the framework down and reset it.
As of late MacIssues peruse Ken H. wrote in about this issue happening on a Late 2013 model iMac, running the most recent forms of Yosemite and all other introduced programming. While the framework would wake appropriately if instantly put into rest and after that woken, if left in rest mode for a drawn out time, then it would basically decline to wake up. http://mac-technical-support.com/
By and large, this kind of issue proposes a force administration issue or other equipment based design blame that can more often than not be handled by the bland investigating ventures of resetting the Mac's Parameter RAM (PRAM) or its framework administration controller (SMC). However in spite of Ken resetting the components, the issue kept, proposing the default values for these controllers is permitting the issue to endure.
In the wake of exploring this issue further, Ken discovered it rotates around the treatment of hibernation mode.
At the point when your Mac dozes, it will at first enter a standard low power rest mode that keeps memory dynamic so you can rapidly continue your work. In any case, if force is lost in this mode then your framework will lose its memory substance and need to begin move down starting with no outside help. To keep this, hibernation mode (otherwise known as standby mode) will compose the substance of memory to your Mac's hard drive and afterward stopped, permitting you to resume work even with lost force. Since this mode utilizes no force, it is required to be on of course for a few frameworks in a few nations. http://mac-technical-support.com/apple-laptop-support/
Tragically it creates the impression that a few frameworks may have issues with hibernation mode, so in the event that you are discovering your Mac not able to wake from rest, then are three potential fixes you can attempt:
Turn off framework hibernation
Since hibernation mode's lone genuine advantage is to permit you to continue from rest even with a force misfortune, a straightforward arrangement might be to turn hibernation mode off by running the accompanying two charges in the OS X Terminal (enter your secret key when prompted–it won't appear):
sudo pmset standby 0
sudo pmset autopoweroff 0
These orders will kill the equipment settings that will put your Mac into hibernation mode. The first is Apple's fundamental standby mode alternative, and the second is a usage required for European vitality controls. To invert these orders, you can again either reset your Mac's framework administration controller, or re-run the orders however utilize "1" as the worth rather than "0."
Also read about common Mac issues and their solution http://mactechnical.kinja.com/how-to-fix-common-mac-problems-1774198819
Debilitate and re-empower FileVault
The written work and reestablishing of memory substance from circle may struggle with FileVault or other full plate encryption schedules. Actually when waking from sleep mode the framework ought to permit you to verify and afterward stack the substance of the hibernation record, yet in the event that a bug keeps this from happening, then your Mac will be unable to stack the hibernation document, and could hang.
To ideally defeat this, first have a go at handicapping your full-circle encryption schedules. After your plate is completely decoded (this may take a while) test rest mode to check whether it works legitimately, and after that re-empower circle encryption and test once more. http://mac-technical-support.com/macbook-support-help/
Expel you’re the framework's hibernation document
A last approach you can attempt is to expel the framework's hibernation document, which is the shrouded record that is composed to at whatever point your Mac goes into hibernation mode. While the framework will reproduce this record on the off chance that it is missing, if introduce then it will simply keep in touch with the current document. Therefore, any harm to this document may keep the framework from understanding it when waking from rest. To alter this, you can constrain OS X to reproduce it by erasing it, which should be possible by running the accompanying summons in the Terminal:
Again supply your watchword when provoked, and after that check whether sleep mode works appropriately.