I am facing that problem with a Geforce4 420 Go. When Xorg (6.8.2) goes into stand-by, suspend or off, it does not turn on, no matter how much I move the mouse or touch the keyboard. I need to press Ctrl+Alt+Backspace to restart X.
I even logged in through SSH from another machine and ran:
xset -display ":0" dpms force standby
The result is the same.