How to diagnose crashes?

[Chris Burchell]

My FreeBSD 5.3-RELEASE box seems to be spontaneously restarting from
time to time.

I have not yet contacted the colo facility to determine if it's a power
issue, but wonder if anyone can help me out in how to diagnose whether
or not it's a server crash and not a power problem.

Where should I look for tips / hints that might help me determine the
cause of a crash that forced a reboot?

Thanks,
Chris