LInux: How do I diagnose / isolate what's causing "random" hangs and spontaneous reboots?

There's good advice from the Debian Administrator's Guide here: http://www.debian-administrationdotorg/articles/492

"Have you tried re-seating your memory, processor, and other chips? Also, you may want to try running another OS (FreeDOS) to eliminate some possibilities.

As a tip, you should also be able to use two monitors quite nicely through Gnome without using the nvidia drivers."