Mac Pro freezes while asleep and fans go to high

Question

I'm not sure if this is a problem specific to my Mac Pro Dual Quad Core MacPro3,1, but it has carried across an update to 10.6.5 and through a reinstall of Snow Leopard. Also, I don't have it on my MacBook Pro. So, I'm posting it in the Mac Pro forum.
Periodically (but now more frequently), when I go to my Mac Pro in the morning, after it has let itself go to sleep, the fans are on high and the machine won't wake up. I can't mount the machine's hard disk remotely from my MacBook Pro on the home network (which I usually can) and I have to hold the power switch down to force a restart. I've checked the Console logs (all messages) and the last message is usually sometime in the morning, sometimes as late as 5 or 6 am. But, there is no common thread to the last messages before the machine freezes, so I can't use that to identify what process was running when the machine froze.
This past weekend, I got up at 5:45 am and heard the fans running high and then went to watch the Formula 1 race on TV. The machine was frozen again when I got back to it at 8 am. So, the problem will happen whenever it wants, but only in the night (before 8 am and after midnight).
I've tried the following, with no success:
• Reinstalled OS X 10.6 and followed the update path
• Reset the SMC and PRAM
• Rebooted the machine before going to bed, so that no user login process or software was running at the time of the freeze.
What is a good process to use for debugging this problem, from this point, since the Console Logs don't give me any consistent information? Is there a way to make the Console logs more verbose?
How can I get a list of all the maintenance processes that autostart on my machine at night? I'm assuming the problem is with a process installed by third party software, since I didn't clear the problem when I reinstalled a fresh copy of OS X.
Thanks, in advance, for your help.

Answer 1

I can't believe I missed this thread. I was sure I was the only one. This has been happening to me for months now, and of course out of warranty. I've tried so many things. Mac Pro Dual Core Intel. Fans go bananas for no discernible reason (according to Activity Monitor). I often return to an un-wakeable display despite the fans going full blast. Sometimes while I'm working, the thing just puts itself to sleep and doesn't want to wake up. Several times a week, the system hangs. (There's usually nothing complicated being done, although using iPhoto is pretty much guaranteed to freeze everything.) Almost always takes more than one hard restart in a row to get it back up, sometimes a DOZEN or more. Have no idea whether attempting a safe boot helps reduce the number of tries but it seems to. It's set never to sleep; I've reset the SMC and PRAM and deleted video preferences (see http://support.apple.com/kb/HT1573). The issue pre-dated installing Snow Leopard and was unchanged by it.
By the way, the computer is at its most silent now - 600rpm each on power supply and exhaust fans, and 500 each on CPU and expansion according to iStat - and it's still pretty loud. Anyone else have that issue?