Mac Pro 2008 shuts down during sleep

May seem unlikely, but there was an EFI/SMC firmware update a couple months after the 2008 model first shipped to cure a common "freeze/restart on wake from sleep" issue.

1000VA/800W UPS or larger is a must due to unusually large inrush current they exhibit. Also can be affected by what else shares the same circuit.

Resetting SMC would be first step.

Trouble is, that these events can be causing lost or corrupt data or to the directory, and you are better off with Disk Warrior or something else than with Apple DU First Aid repair.

I have the same problem, my MacPro 2008, no more sleep when I tried to go to sleep mode then, will shut down instead. It was happened after installed MacOS 10.6.4, please any idea, please, I need help.

Komson

Get a 1500VA if you don't, an APC SMART 1000VA also. Good insurance.
What else is on the same wiring circuit... Maybe it overloads the circuit.

As mentioned elsewhere multiple times, those systems have an excessively high inrush current and the forum was littered with threads back in March 2008.
http://en.wikipedia.org/wiki/Inrush_current

And try the new method for SMC Reset which is 10 second power-on with power cable unplugged.

I have the same problem on my MacPro 2008 after updating to 10.6.4.

I jave done troubleshooting, but it still shuts down when I ask it to sleep.

Odd problem.

Using the menu bar to sleep, the machine sometimes will shut off immediately. Sometimes it will enter sleep, from which it will occasionally wake normally and sometimes shut down.

Though energy Saver settings are set not to sleep the machine, it has slept once and shut down once after sitting for an hour.

Worried that continuing this will hurt my hard disk (have just replaced a faulty drive), I now plan my computer up time so as to avoid the issue if at all possible.

Have a good warranty program through my reseller here in Japan (five years) and have some trouble with the power supply fan being noisy, I will send the machine to Apple next week and add this problem to the list of things to check out.

Whew, I thought I was the only one with this problem. I'm also getting the "double-click" sounds when trying to wake the machine up from the dead zone (after going to sleep- either on its own or after attempting to awaken it a few minutes after manually putting it to sleep).

I've had my computer serviced by a Mac-authorized repair center three times for this issue. The first visit resulted in an operating system upgrade to Leopard, which seem to fix the issue for a few days. When it reappeared, the second visit resulted in a logic board switch- the technician actually kept it there because the problem reoccurred after testing the new board. He then found a broken wire in the power supply and replaced that. On the third visit, they actually had to send it in to the Apple engineering department- who replaced the video card with an updated version of the same.

This is driving me insane- the repair center knows their stuff (I'm in IT, myself so I know they're not incompetent)... they've exhausted nearly every possible solution- replaced every component, different OS, etc... the apple engineers couldn't even fix it. I dread going to the Apple Store because I know the people at the Genius Bar are way less knowledgable than the guys I go to... but since I'm still under AppleCare, I may be able to get a machine swap if they can't fix the problem in a few weeks.