Power Mgt: "Turn off monitor" "Never" always reverts to "After 20 mins"

I have a Acer Aspire L5100-TV with Windows XP SP3 and full hd tv connected via HDMI. The monitor is switched off after 20 mins with no keyboard or mouse activity, it is always frustrating when watching TV or movie. There are no screensaver used. Checked in Power Management and setting to "Turn off monitor" is never in any power scheme does not help, for some reason this setting always reverts to "After 20 mins" if checked later. Can anyone tell me how to solve this issue? Thanks.

It seems to me like this problem is caused by the Acer Power Management Utility running. You can check the system tray which is located at the right hand side botom for the Acer icons and define the power preference there.

Thanks for the reply, but after I replaced the Acer supplied Vista with a Windows XP, no Acer utilily are running. I think that there is some setting in BIOS that I need to check. The problem that I am facing is weird because only after 30 minutes it reverts only after playing the VLC Media Player when it starts playing a movie. So, if no movie is played, then the monitor stays on forever.

Did you ever find out why this happens?

I have the same problem when running videos, that pwr management monitor setting is changed to 20mins