I've got Ubuntu 9.10 on a Dell Vostro 420 desktop, a little over a year old, which I use for plain vanilla work stuff (email, web, terminal, text editor). Every now and then, at totally random times, it completely freezes on me. Hard. Mouse and keyboard stop working, cursor stops blinking, clock stops moving. All I can do is hold down the power button on the front of the box to shut it off.
Sometimes it happens after several months of continuous uptime; sometimes it happens a few minutes after a reboot, while all I've done is open a terminal to look at log files, or maybe firefox to do a google search. Each time, there is nothing at all in /var/log/messages at the time of the crash. This makes it seem like a hardware problem, and indeed a few months ago I opened the box and wiggled everything and the problem went away for a while. But now it's back. I went in and checked everything, took out each RAM card and reseated. No luck. I ran all the system diagnostics (the long version) and everything passed with flying colors. Something is messed up in this box, but without any useful logs or failed tests, how in the world am I going to find it? And of course, Dell's not gonna help me cause I went and replaced Windows with Ubuntu.
What steps would you take next to track down this problem?