Need help with Reboot cause

[Peter J. Stieber]

This is going to sound vague, but here goes...

I have a dual opteron system that has been acting as the worldly node 
for a small cluster of computers since September, 2004.  The machine is 
running the latest x86_64 Fedora 10 kernel that I recently loaded (April 
2).  The machine reboots without warning.  I can't find the cause in log 
files (maybe I'm not looking in the correct log).

I'm currently running memtest.  If all of the tests pass, could the 
community suggest other diagnostic tasks or information I could post to 
help diagnose the problem?

I wish I could be more specific,
Pete