System goes to lunch after about 24 hours

I'm all for giving people, and even machines, a rest. But for some reason, my HDD installed Knoppix 3.6 is exhibiting some odd behaviour if it's left on for long periods of time. What happens is that the machine eventually blanks the screen after about 30 minutes of inactivity, and works fine if I move the mouse or hit the keyboard to wake it up. Even leaving it this way over night is not a problem.

But after about 24 hours of operation, something kicks up on the machine that eats CPU and has the HD going crazy to the point where it's almost impossible to even shut the machine down without unplugging it or holding the power key for several seconds. Because it is so non-responsive in this state, I can't even get a ps -ef to give me a result in a terminal session I left open.

I normally use the XFCE desktop that comes with this version of the distribution, and I'm wondering if that might be having some wierd interaction with some power setting or KDE setting or...

Any ideas?

Possibly some daily crontab job (e.g. updatedb)?

Are there daily cron jobs setup by default?

Regardless, I suppose that would be a good place to start looking. Thanks for the idea!