U/I freezes, mouse moves, keyboard ignored, can still remote login

Question

Hi...
Maybe someone has seen this before. I've been stumped for 9 months with this problem.
Aproximately once a month (or two months), always while using my computer, the whole U/I freezes -- although mouse motion works. All other U/I updates are frozen. The clock freezes, iTunes goes quiet, all dynamic updating of the screen (weather, processor use, etc.) all freezes. Only the mouse pointer moves around.
Every time I can still ssh into the machine from my laptop !! The load average is near zero. I can run "top" and only top itself is consuming processor time. One time I believe I was able to kill a system process, I thought it was CoreGraphics, and regain control at the console. But I must have forgotten, because this hasn't worked lately. Also, one time I thought that after waiting a long time, the screen recovers. But usually I don't have the patience to wait - so haven't confirmed.
Typically I do a shutdown -r to restart at this point. Although last night I was randomly killing system processes and ended up being unable to sudo anymore (would just hang after asking for my password.) So I power cycled.
Being that this happens so infrequently and I can't reproduce at will, I must admit I haven't kept due deligence on what I'm doing. Often it seems I'm launching a program. Last night I was launching EditCSS for the first time. All seemed to freeze instantly the moment it was up. It was at that point I couldn't do anything at the console.
There is absolutely nothing written into the system log during this time.
I have run hardware test over the months. All is okay. My RAM is dealer installed. My G5 has been in the shop previously and extensively diagnosed for an overheating processor in the past (the processor was replaced.) So I assume it has been through full hardware diagnosis a couple times. The U/I freezes were happening before this period and after.
The U/I freezes have also occured through Mac OS X updates. I always am hoping they'll stop after an upgrade, but that hasn't happened.
I'm always running Deja Vu, Little Snitch, Menu Meters, PowerChute, Adium.
Any other suggestions, ideas, or experiences others have had?
Thanks,
Erik
Quad G5   Mac OS X (10.4.8)   4.5 GB RAM

Answer 1

Well gentlemen (and ladies, assuming there are some here), to throw another “stumper” into the fire here, I have a late-model 2.3GHz G5 PCI Express Powermac, and I literally have had it running under FULL CPU UTILISATION (distributed.net RC5-72 client) 24x7 since I received it in the fall of last year. It is a refurbished unit, and in January of 2007 I added an ATi Radeon X1900 PCI Express card to it… well, the only time I get these UI freezes (where the only thing responding is the cursor) occurs within UI-related accessing in a game called Tribal Trouble. Specifically, when accessing the options or campaign settings, sometimes everything else locks up (except for the mouse and background music). I have not yet tested with the stock GeFarce 6600 card in it, perhaps I will give that a go. Otherwise, seems to be a common issue with you all.
Oh, just to be sure—are you who are affected by this problem using the AGP or PCI-Express G5 towers?
-he who stacks pork
dual-core G5 2.3GHz / two dual 1.42GHz MDD / two GigaE G4 / 1.5GHz G4 MacMini   Mac OS X (10.4.9)   Two of everything; dual dualled duals (duelling duals)