How to disable the power management in fedora 12, so that lcd/monitor should not go to sleep/off when system is idle?
Do you want to just disable this sometimes?
What desktop environment are you using? Gnome has Gnome-power-manager, which allows you to control how the monitor behaves when the machine is idle. In KDE, powerdevil is part of the base, so opening the systems settings (Advanced tab) should get you to the power management settings.
An extreme approach would be to turn off APM and ACPI completely. Turning off APM and ACPI will disable all power management on your computer - on a laptop, you are going to kill your battery performance. That said...
To do it only once:
If that works, you can make it permanent:
Following are commands to successfully disable the Power Management in Fedora
The following will set DPMS(Display Power Management Signaling) parameters
The three zero values represent three different modes
The following will disable the screensaver
For details please see