Dual G5 1.8 GHz screen/keyboard freezes (new with 10.4.6)

Question

Three times in the past month the screen and keyboard on my dual 1.8 GHz G5 (first generation) have "frozen" as I closed windows or Command-tabbed between running applications.
When the screen and keyboard are frozen, the menubar clock does not increment, but I can still move the cursor across the screen with the mouse. The machine itself is not frozen. I can log into it as a server from my MacBook Pro, read files from its hard drives and write files to its hard drives, but I cannot do anything from the machine's own keyboard. If I press the "sleep" LED on my Apple LCD display, the LED dims but doesn't extinguish, and the machine doesn't sleep. If I hold down that LED on the monitor, the machine will power off. On reboot, the recovered files folder in the trash holds six files whose names all start with "dftmp" (five of the six are named dftmpGELNNHAM with some subsequent lower case k and other characters, the sixth dftmpCPEMKHAM, also followed by a string of k and other lower case characters. The Recovered Files folder in the trash also contains a SENDMAIL folder, which is empty.
One diagnostic suggestion I received was to open Activity Monitor and the Console to see if anything unusual occurred (spikes in processor usage or RAM usage, for example). I have the logs, and just a few minutes ago another freeze occurred (the console's display and the Activity Monitor display freeze along with everything else). I'm not capable of interpreting the logs.
Rebooting after this most recent freeze, the CPU usage bar graph now shows the two processors alternating in rhythmic spikes of CPU usage by System (from a low of 5% to a high of more than 30%, the spikes being about 18 seconds apart per processor (so total System CPU usage peaks at 30% or thereabouts every 9 seconds). My sense is that this is not normal, and my MacBook Pro certainly doesn't do this. At the moment, the only things I'm doing on the machine are typing this message, downloading in Thoth, and watching the logs and Activity Monitor.
Is anyone interested in looking at my console logs? Is there someone else I should report this to? It's not something I can show to my local Genius, because this has happened only 3 times in a month. On each occasion, the freeze occurred when I was closing windows or changing focus from one window to another, but I cannot reproduce the freeze at will.
Thanks so much,
1,8 GHz dual G5   Mac OS X (10.4.6)   Dual G5, 2 internal drives, 2.5 GBytes RAM, ATI X800XT graphics card, 2 displays
1,8 GHz dual G5   Mac OS X (10.4.6)  

Answer 1

Try using Disk Utility to repair your startup disk (hard drive) as shown in Dr.Smokes Resolving Disk, Permission, and Cache Corruption and see if that helps.
Cheers!
DALE