Box Mysteriously Rebooting?

[Jeff Bethke]

Hi All,
   I have a  host that has been super relilable without issues.  Then, I 
had a power outage. After that, the host has stayed stable for anywhere 
from 6 to 48 hours... Then the host mysteriously reboots itself.   I 
swapped out the power supply (figuring a fried power supply could 
possibly be the culprit) and yet the problem persist.   Where do I look 
to figure out what's broke? Nothing in the logs. The console log doesn't 
show anything. dmesg looks kosher.   Its as if someone hits the power 
switch!  Anyone have any suggestions on what tools I could use to 
pinpoint what is causing the reboots?

Help?

Thanks!
-jeff