iMac not waking up from sleep after Yosemite upgrade

I have resolved my issue.

In System Preferences -> Energy Saver I disabled "Wake for network access".

I have had it disabled for several days now and have not had the problem reoccur.

I had originally turned on "Wake for network access" to allow usage of Air Video Server HD when my iMac had been put to sleep.

Hopefully in a future update of Yosemite this issue will get resolved.

This is exactly what is happening to my MBP. I just turned off the screen saver and set the display sleep to NEVER and the problems has not come back...so far.

I too have been having this issue since the Yosemite update. (27" iMac mid 2011, i5, 12gb)

Unfortumately, the "Wake for network access" has not worked for me. Thanks for posting a possible solution though.

If my computer is awake, I always use the keyboard to put to sleep. In future, I'm going to try going through the Apple logo

I think I found a pretty easy work around. In system preferences>energy saver I set my computer AND display to never go to sleep. unchecked "put hard drive to sleep." Then have my screen saver set for 10 minutes. Problem seems to have gone away.

Unfortunately I need to retract my comment about resolving the issue above:

>>

I have resolved my issue.

In System Preferences -> Energy Saver I disabled "Wake for network access".

<<

The problem is happening LESS. But it has not stopped. It has happened three times now in the last week. But it does seem to happen less often after the above change. I am going to try setting System Preferences -> Energy Saver -> Computer Sleep and Display Sleep to "Never" and see if that helps.

I've been good for at almost 2 weeks now. Unchecking all options in System Preferences -> Energy Saver options and unplugging all usb ports before putting my iMac to sleep has done it for me.

Going through the Apple logo hasn't worked either.

Does anyone else have a TB drive hooked up? I have turned mine off (but left it plugged in), and everything seems OK.

Only time will tell though, so I will update later.

Problem is still happening for me. The latest thing I tried was making sure my fitbit/USB device was not plugged in when I put the iMac to sleep. But just this AM I woke it from sleep and the screen would not light up so I had to force it to reboot (holding the power button down on the back of the iMac).

I do have a Thunderbolt Promise array plugged into this iMac. I am going to start shutting that off before I sleep the iMac and see if that helps.

I should also mention I have not tried turning off System Preferences -> Energy Saver -> Put hard disks to sleep when possible. I'll try that next.

I thought it was fixed on my end but it isn't. One top of that I've had Yosemite crash once or twice a week for no apparent reason.

I've had my TB drive (a 3Gb LaCie D2) switched off (but still connected) for nearly a week now. My Mac has been going into sleep mode itself, and I've been forcing sleep mode with Opt+Cmd+Eject (about 5 times a day) and I have had no problems at all with wake-ups.

TB drive is now back on. Watch this space.

With TB drive now connected and switched on, the problem has returned 😠

Interesting reading your experience. I thought the only solution was to update my 2011 iMac. I won't now. I'm not sure if the iMac is sleeping when it won't respond to a key press or mouse click on a black screen as the external drives connected are spinning. A cold shutdown down and reboot is the only way right now to get into the iMac!!!!

I turned off my TB LaCie drive and that eliminated the problem for me as well. Not a great solution. Hope they fix this soon. :-(

My 1TB Thunderbolt Buffalo drive is my Time Machine, so don't like the idea of disconnecting and remembering to reconnect every time, but maybe better than cold booting the machine. I'll give it a try.

Yeah, feel the same way here, but I was starting to get concerned about all of the cold boots so at least there is a semi-acceptable workaround in the meantime while they finally fix this issue. It's overdue IMNSHO.