MacPro 2008 after Mountain Lion update has major sleep problems

Question

I have a 2008 MacPro with 2 2.8 quad-core xeon processors, 6 gigs of ram, and an Nvidia GeForce 8800GT graphics card.  On Wednesday, I updated my Mac to Mountain Lion and subsequently found one minor improvement and one major problem.  The one improvement is that sleep now works again automatically, if my MacPro is idle for a while (prior to this, I had to push the power button to put it in sleep mode).  The major problem is that after a while in sleep mode, the fans activate and don't stop and the Mac becomes unresponsive, forcing a hard shut down.  Although I assume that this is unrelated, just in case, the only other additional change this this week is that I got a Time Capsule.  Any ideas or suggestions about what to do are much appreciated.

Answer 1

Power nap and mac compatibles
By crispin. Original by Lionel - 28/07/2012 08:02:00 CEST - Category: Laptop
Here's a little feedback on Power nap, one of the new features brought by Leo. Let's start with what Apple says about:
When your Mac goes to sleep, it continues to work with Power Nap. It regularly updates Mail, Contacts, Calendar, Reminders, Notes, Photo feeds, Find My Mac and Documents in the Cloud. Connected to a power source, your Mac will download the software updates and performs backups with Time Machine. During all these updates, the system sounds are silent and no light, no fan will be triggered, so nothing will disturb you. And barely awake, your Mac is ready to go.
It must be added to this information: Power Nap requires a Mac laptop with flash storage. May rneed an updated firmware.
In fact, Apple has proposed specific updates for the MacBook Air in 2011 and 2012 and for the MacBook Pro Retina. However, as related by OWC, other Mac are compatible such as the MacBook Air 2010 13 "(not 11"). It is possible that this is the case with other Macs with SSD, but it will need to be checked case by case.