First off, what I have:

I installed an old copy of Mandrake 8.1 (didn't want to dl a whole new distro), and then dl'd and compiled the sources for Kernel 2.6.5, X.org's release (as of May 10th, I don't recall the exact version), GCC3.4, the NVidia driver for my GeForce, and Gnome 2.6.

Now, the symptons: If my computer sits idle for a period of time (more than an hour, but the exact time is uncertain) it will hang as if shutdown were called without -h.

The system is entirely unresponsive. Various three fingered salutes do nothing. I must use either the reset or the power buttons to halt the system.

If I am running a CPU intensive program (ie, POV-Ray) it still crashes, but not as often. It is possible that it is hanging after the program finishes.

There is nothing in my system logs concerning a shutdown. When I reboot (either from the harddrive or a burned copy of Knoppix) and examine the logs, it is as if they just stop.

Booting Knoppix off of a CD, I can leave the computer on for days without a problem.

Does anyone have any ideas what this might be caused by?

I will try to get more accurate timings when possible, but this is difficult as it always happens when I am away from the computer for an extended period of time.

Thanks in advance,

...Chambers

dunno what's going on but have you tried leaving your on computer without X? You can stop X by going to a text terminal with ctrl-alt-F1, and then do
init 3
as root. Just to see if it is X that's crashing or something else.

Since you've upgraded big parts of the sysem, have you upgraded all other dependencies ? The 2.6 kernels need some other up-to-date binaries, and i guess so do the rest of the stuff you've installed.

Maybe some power-saving software coming up and crashing ?

You mean [Ctrl]+[Alt]+[Del], or the [SysRq] keys ?

A way to look into this would be to log into your machine from a network, before it "crashes", and to see what happens.

I mean the SysRq keys.

I can't log in from another machine, because it's the only one I have (and I don't have 'net access at home, only at the library).

I'll try leaving it on without X to see if that does anything...