Twice now in the last week, I have come into work and our linux email server has stopped responding. Can't log in via vnc, SSH, or the console. It is totally unresponsive. I've messed around with linux before and can get around, but I have no idea where to start looking to figure out what's going on. I've checked the log files in /var/log and didn't find anything unusual (other than massive amounts of failed authentications). Where should I start troubleshooting this?
Thanks

In my experience, totally frozen usually points to hardware. Any recent changes?

That's what I was thinking, but unfortunately, no - there have been no hardware changes. The only changes that have been made are that I have been in the system setting up a test website using the Interchange framework. Unfortunately, I had already caused problems. The version of Interchange that was set up required non-threaded perl or a newer perl than was installed. Not knowing that Spamassassin required perl, I uninstalled the one that was there and installed the very latest. It would send emails fine, but when the power went out later that night, our email was down when the server came back up. Uninstalled the latest and installed the original and it worked fine. Until a few days later when it just plain didn't respond. I came in the other morning and it happened again. I'm thinking of taking in an Ubuntu CD and running it through the Mem tests.

On another note, I have had problems installing the perl modules Math::Fraction, Math::BigInt and Math::BigFloat. The tests fail. Would that indicate bad Ram or CPU?