Diagnosing an unstable machine

[Ross Penner]

I'm currently using FreeBSD 6.2 to run as a fileserver and gateway for my
home. It's been incredibly unstable and I'm trying to figure out why. What
can I do to try and figure out what is causing these crashes? Apparently the
machine just rebooted 20min ago looking at the uptime. They're seemingly
random to me as there is definitely no usage pattern that is obviously
bringing these crashes about. Any help I could get would be greatly
appreciated.