Description of problem:

In fc4test3 and now in fc4 my system will freeze.  When this happens the KDE
desktop display freezes and the mouse and keyboard stop responding.  I have let
the system sit for as long as an hour without it recovering.  When this happens
I cannot ping or access the system through ssh.  I have run memtest on my system
 memory and it passes.  I have examined the logs in /var/log for messages at or
near the time of the freeze without finding anything.  I am unable to relate the
freeze to any particular action or application but it always occurs when I am
actively using the system.  I have never experienced a freeze while the system
was sitting idle.  Freezes occur seemingly randomly, I may go for a day or two
without one, I may experience several in one day.  I have no idea how to proceed
from here to determine what is causing these freezes andy guidance on
troubleshooting procedures would be appreciated.

How reproducible:
  I am unable to reproduce this problem predictably

My system:
CPU: AMD Athlon 64 Processor 3500+
Motherboard: ASUS A8N-SLI
Video: Triple headed system using two Jaton PCI video cards with NVidia
GeForce4 MX 440 AGP8X chips and NVIDIA's proprietary driver as packaged by livna.org
Memory: 2GB DDR-RAM
Storage: 120 GB Serial ATA drive using sata_nv driver
Audio:  Realtek ALC850 onboard chip using snd-intel8x0 driver
OS: FC4 - 2.6.11-1.1369_FC4 kernel