black screen on f16 laptop after idle

[Peter Gueckel]

I powered up my laptop. The kdm screen was there, but I did not log in. After 
some time, perhaps 20-30 minutes, I was ready to log in. The screen was black, 
but that occurs after idle, so no problem, just wiggle the mouse. Nothing 
happened. The screen stayed black. I know the password field was focused, so I 
typed it and the computer logged in. Still black screen. I typed ctrl-alt-f2 and 
logged in as root. Still black screen. I typed reboot and the computer rebooted 
and I again had a visible screen.

How can I wake up the display after it has gone into a sleep mode?