Mountain Lion won't sleep

My Mac Pro also won't sleep. When I hit the sleep button, monitors will turn off, but the tower itself keeps running. Do you have any pci-e cards installed? I know they can lead to problems with sleep.

I figured mine out. I had Internet Sharing turned on. This is what solved it for me: http://www.adeepbite.com/lion-seems-having-insomnia-it-doesnt-sl

You Can Go to system preferences energy saver put sleep on. Hope This Helped 🙂

BennyM suggested running a terminal program to identify the cause. This worked for me.

Run the pmset command in Terminal to find out what is preventing the computer from going into sleep mode, fix the issue and then confirm that the problem is resolved.

To find out what is preventing your computer from sleeping, open Terminal and run:

pmset -g assertions | grep Sleep

You'll see something resembling the following:

PreventUserIdleDisplaySleep 1

PreventSystemSleep 0

PreventUserIdleSystemSleep 0

pid 524(screensharingd): [0x0000000500000202] 21:01:53 NoDisplaySleepAssertion named: "Nameless (via IOPMAssertionCreate)"

If any of these are set to '1', then some setting or program is keeping your computer from sleeping; the perp will be identified in the last line of output. In my case, the 'screensharingd' program is to blame. I assumed that this program is related to Screen Sharing, which I had turned on.

I need Screen Sharing on this computer, so I went to Preferences>Sharing, clicked off Screen Sharing and clicked it back on.

To confirm that the problem was resolved, I reran "pmset -g assertions | grep Sleep" and got the following:

PreventUserIdleDisplaySleep 0

PreventSystemSleep 0

PreventUserIdleSystemSleep 0

Final confirmation: my display was able to sleep on its own again.

I hope this works for you.

I'm on a MacPro and sleep did work when I installed ML but then out of the blue just quit.

The screen would go black but the system would not go to sleep (white LED stayed on full, touch a key and the screen lit right up, wasn't sleeping). I tried everything, cleaned out all my preferences, went through all system preferences a dozen times, deleted a couple of apps that I had recently installed.. on and on and on, for days. I even reinstalled the update (that was already installed) OSX 10.8.2 overtop of itself hoping that would work out the kink.. Nada !

I could boot up from a separate bootable hard drive on my MacPro (holds 4) and it would go right to sleep, using every different command there was to put it to sleep but as soon as I switched back to my main system hard drive.. Nada ! I was just ready to run the terminal check (stated above) but was holding off cause I am not totally up on using it, have in the past but only once a couple years ago.

I even tried setting up a new user account and that wouldn't work either. Then I saw one of the above posts that said they had print sharing turned on and that solved their problem. I checked but I didn't have any settings of any kind turned on for sharing and I'm the only user of the machine.

THEN (don't ask me why), I remembered that a couple of days ago I got a warning from my Epson Wireless NX430 printer that I was low on black ink. It still printed fine so I didn't change the cartridge, wanting to drain every last drop out of it because they cost so much. So I sat there and said to myself.. I wonder.. No, it couldn't be. So I went to my Epson printer and everything looked fine, it was in the sleep mode as it usually is when not being used.

I hit the power up button and lifted the cover to change the cartridges (decided to change the black and cyan since I was doing it as both showed low). I changed the two cartrideges, closed the cover, the printer ran through its "charging cartridge" function. I came back over to my MacPro and hit the Opt + Command + Eject key and my MacPro went right to sleep, didn't hesitate for one second, went to sleep mode and the white LED on the front of my MacPro went into pulse mode (instantly) showing it had shut down and was sleeping comfortably..

UN-FRICKIN BELIVEABLE !!!!! Days wasted, programs trashed, clumps of hair on the floor ALL FOR NOTHING !!!! Hope this helps somebody else so you don't have to go through this mess !!!!!!!!!

@reagan9000 Thanks for the "pmset". That helped me track down my culprit which was time machine.