Hello,
I have a server (Dell PowerEdge 9550, if I remember right) running CentOS 6.0 in the GUI mode (Gnome).

I have disabled all screen saver and power-saving options, as well as completely remove the power management modules, but I keep running into this problem.

What happens is, if a "vncserver" session is left running for multiple hours (not exactly sure what the time frame is, but somewhere within 12 hours), the server will go into a hibernate-like mode. At this point, all remote services are disabled, and a friend has to manually power cycle the machine since the keyboard and reset button seem to do nothing (power light is on, but no HDD activity).

I connect to this server with SSH, then tunnel with VNC to control the desktop environment. I've discovered this problem when I've left the session open so I could return to my testing, but we do hope to turn it into a production server for a university project.

I just did a test of this last night and its locked up again -- no programs were running, just the VNC service.

Any ideas? Where should I be looking in logs for this? Has anyone even heard of a problem like this before?

Thank you!

I assume you have looked at a console and the system didn't just crash? A sudden crash won't make it to /var/log/messages. You need an attached display, serial or network console window open.

Dell PowerEdge servers have a service processor with lots of configurable options. Make sure there isn't some inactivity timer turned on that is putting itself to sleep. While you're in there check the event log. It also lets you change the power/reset button behavior too.