I have a bit of a strange problem that just started happening recently. Out of nowhere Ubuntu 11.10 will just shut down.

I don't think its hardware because I can't find any information in the logs. I don't think its temperature because I monitor my temps and my machine is liquid cooled. The pc continues to run while the OS shuts down so its not being interrupted by power where all of a sudden everything just loses power. I don't really overload the machine at all, I mostly just code on it, but I do have apache2, tomcat, james email server, and mysql running on the system and they are auto started. I don't actually have any traffic coming into the machine though, I use it specifically for development.

Edit from comments:

It's not really going to a shut down screen, the screens go black and
the computer still runs, but the actual OS shuts down because if I'm
listening to music or something, the music will skip a few times and
then stop. This is how Ubuntu normally shuts down for me so I assume
its a software shutdown. It's not following a pattern unfortunately,
it's random and sometimes within a few hours of the last time, other
times its days between. Normally when I am on the machine.

Any ideas on how I can diagnose a problem like this? Does this sound like a memory leak issue?