I finally upgraded from Fredora 11 to 15 and experienced the problem described below. Then, I upgraded to Fredora 16, and am still experiencing the same problem. Both upgrades were clean installations from the respective Live File System. The machine is a Intel Dual Core Dell Dimension with a Intel 865 Chipset with 128M.
In the Screen Settings there is a setting for Turn Off After. Whatever that value is, my machine turns the monitor off at that time. But, I cannot get back into the machine via the console or the network. The monitor stays off, when I move the mouse or type on the keyboard. Additionally, the network interface goes down, so I can't even ping the machine. It does not matter whether the Lock setting is On or Off.
I am sure that there is an easy fix to this, but I can't find it in the archives here or by searching Google.
Any help is appreciated.