It might be instructive to look in /var/log/messages to see if the kernel managed to notice anything awry just before the crash. [I know, I think you've already done this, but without any clues to go on, I don't think other people are going to be able to do any better than you.]
It might also help to go through a complete inventory of your hardware. For that matter, it might help to just remove boards from your system to see if that makes the problem go away - anything to isolate the problem is good. -- Raul
