...or not. My iMac occasionally fails to wake from sleep no matter how much I move the mouse, mash the space bar or verbally encourage it. Requires a forced restart via the power button. I can't identify any particular activity on my part that could cause this and I've trawled a few other fora (ums?) for an answer but without success.

My Energy Saver prefpane is set for 1 hour Computer and Display sleep and all the boxes except "Restart automatically if the computer freezes" are ticked. Hmm, might tick that one too if it automatically restarts on failure to wake!

An occasional restart isn't such a bad thing but I would prefer to choose the time. I wonder if any contributors to this venerable forum have any clues?

Andy

iMac 21.5 in, late 2009, 3.06 GHz, Core 2 Duo, 8GB, Lion 10.7.1

I often find the return (CR) works when nothing else will and so far it has created no I'll results.

I've occasionally observed the same thing in my MacBook. When it happens, hitting the Return key usually does the trick.

Yep, tried hitting Return too but that doesn't work for me.

CR? Is that short for the old typewriter Carriage Return from days of yore?

Yep it is

First line of duty is to make sure the computer is managing to get to sleep in the first place. the lack of sleep light on the newer imacs makes this a little more ambiguous though. does it get completely powered down, with fans off? it won't wake if it hasn't managed to sleep yet.

Well, I'm assuming that non-use of the iMac for a couple of hours, a black screen and no fan noise means that it has indeed completely powered down. Normally tapping the space bar brings it to life with no fuss.

I may be on the wrong track but I'm now wondering whether it has something to do with 1Password and its Safari helper app which crashed this morning. 1Password (the MAS version) has been a bit unstable and seemingly inconsistent lately and I'm about to run Agilebits' 1Password Troubleshooting app just downloaded from their website.