Mac Pro won't wake up from sleep with Mountain Lion
Hi! My early 2008 Mac Pro won't wake up from sleep mode now that it has Mountain Lion. I have found it asleep a few times now, and pressing the power button doesn't wake it up. When I manually put it into sleep mode, it has the same problem.
I've set Energy Saver to never go to sleep, and that seems to work, but it would be nice to not have to do that. A friend's identical Mac Pro with Mountain Lion is not having this problem.
Seems you have discovered an undocumented feature aka bug. Many users are having sleep issues with the Mountain Kitty. Some can't get it to nap, others have a variety of issues waking or after waking. This seems to be a software, not a true DIY repair issue.
Apple has issued an SMC update for the Retina MBP which has fixed the issue for them. You should run Software Update and see if there's one for you, too.
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I found the simple fix! my Mac Pro is from mid 2008. After I recently installed Mountain Lion when it goes to sleep it often won't wake up. I would have to force shutdown and restart. I didn't find any satisfactory solutions online. What I discovered though was to go to System Preferences, then Energy Saver and click off all checked boxes. My computer wakes up every time now. Problem solved. That easy!!!
I'm having a sleep issue myself on my late 2008 Mac Pro. It just goes to sleep suddenly and I'm not able to wake it again. I have to force shut down and restart it again. But after a short while it just decides to go to sleep. I'm running the latest version of Mountain Lion 10.8.1
I ran the maintenance software Cocktail on it, but it hasn't helped my Mac Pro.