Why Doesn’t My Mac Wake From Sleep? [Ask MacRx]



When your Mac doesn’t wake from sleep, the reason could relate to uncooperative hardware or unstable software. When people don’t wake from sleep, it could be the sign of a Monday morning or an upcoming exam…

Sometimes when my mac goes to sleep it doesn’t want to wake up and the screen stays black. I have to turn off computer then turn it back on. Why does it do that?


Hi Andres,

Sometimes a USB or FireWire peripheral can prevent a Mac from going to sleep or waking back up. See if things work correctly with no external drives or printers attached. Also run Software Update to get all the latest patches for your Mac.

A crashed or hung program can also prevent a Mac from waking up from sleep. Check your system logs via the Console application in your Utilities folder. Look for any entries about what was running between the time the Mac was last running correctly, and when you found it frozen. You may have a program or background task which needs to be upgraded.

If none of that identifies the culprit, you may have something corrupt in your OS X installation. In that case make a backup of your data, then try reinstalling Mac OS X.


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Readers, have any additional suggestions on this topic, or corrections/clarifications on the advice above? If so, please leave your thoughts in the comments.

  • Leslie Martin

    If Andres is using a wireless keyboard with Lion, there is a setting (that is off by default — why, I don’t know) that will allow wireless devices to wake up the computer, but it has to be specifically set on. System Settings | Bluetooth | Advanced | Allow Bluetooth devices to wake this computer.

  • R.

    Don’t bother re-installing OS X until you’ve tested doing a SMC reset.

    EDIT: meant SMC, not SCM.

  • Adam Rosen

    Robin, what is an SCM reset?

  • R.

    Read this: http://support.apple.com/kb/ht

    Worked for me when my Mac didn’t woke up from sleep.

  • Yacko

    SMC – System Management Controller for Intel Macs only, basically the same as the old PMU – Power Management Unit reset for Power Macs. Shut off computer, unplug for a couple of minutes, plug back in and boot. I don’t think this will necessarily solve the problem.

    A black screen sleep problem has plagued some Mac hardware paired with some OS since the start of OSX. Since Andres doesn’t mention what Mac model, what OS and what peripherals he is using, offering a solution is diffivult.

    I would go with likely a USB device, perhaps a hub. Also best to wake with a wired keyboard or mouse.

  • David S. Long

    Power management, including sleep, charge, wake and shutdown functions are controlled by a the PMU/SMU/SMC. The most common way to corrupt a PMU/SMU/SMC is to plug the AC to the computer then to the wall. One should always plug the AC adaptor in the receptacle first, then your device. PMU/SMU/SMC reset is computer specific, don’t guess, look it at http://www.apple.com/support/ using the name of your computer.

  • Guillermo Tesoro

    if this issue has arised with an iMac late 2011 (it’s possible that this happens with previous models but I can’t confirm) it’s probably a hardware problem. When I bought my iMac this same issue starts to happen. I tried all the workaround and solutions that I can found (SMC Reset, BT configurations, messing with pmset, etc) but finally I carry my Mac to an official reseller and they exchange my iMac with no problem.

    Hope this could help and sorry for my bad english.

  • CitizenX

    Occasionally I have this problem on a late 2009 MacBook.  Usually some combination of enter, space bar, mouse clicks and power button wakes it back up. I’ve never had to shut it down.

  • Craig Doran

    I had this problem with Lion on my 2009 iMac.  Uninstalling the Flash web plug-in fixed it.  It seemed to be related to the iMac falling asleep when Safari was open with a page containing Flash content.  For awhile, I used Chrome to view Flash sites without re-installing Adobe’s Flash web plug-in.  Eventually, I did re-install the Flash plug-in.  Now my iMac seems to have insomnia.

  • Tekk zool

    This happened to me with a mid 2010 27″ iMac if I had anything plugged into usb. I mean anything, even the standard usb keyboard prevented my iMac from waking up. No combination worked, not even holding the power button. I had to unplug the power cord, wait a while and plug it back. I don’t have a clue of why it happened, but it seems to be solved since I updated to Lion.

  • ramunasbl

    I have an opposite problem. My 2010 MP refuses to go to sleep…. and quite often even if I put it to sleep manually I find it awake in the morning….
    Some software keeps it awake… However, if nothing is running it behaves as good boy and goes to sleep as prescribed (:

  • Helen O’Brien

    I believe I actually have the answer (or at least the same problem+a workaround). When I close my macbook (it’s about four years old), the sleep light doesn’t begin pulsing for about five seconds. During this time, you can still hear the hard drive spinning (or whatever). If you move the laptop at this point, the computer won’t wake up. Teaching yourself to wait until the light starts to pulse is a bit of a challenge, but it’s less frustrating than losing the videos you just buffered because you don’t have wireless. . . maybe I’m getting too specific. Anyway. That works for me.