Why does my screen dim on a desktop installation of Windows 7?

Periodically, while using my Windows 7 Pro desktop installation, the screen suddenly dims. The brightness is about 75% normal (estimate). It's as if I am in a power-saving mode on a laptop running on batteries. But this is a full desktop installation.

I know it is not a hardware glitch or monitor adjustment issue because the Windows cursor is still bright white while everything else goes dim.

The Control Panel > Power Options have not been changed. They are set to "Balanced [active]" and I have tried restoring the default settings. Flipping through the power and display settings, everything looks "normal." There is no screen saver or power-off-after settings apparent.

Rebooting the system resets everything to full brightness but I can't find a way to restore it in Windows or to keep it from happening in the first place.

Suggestions?

Are you using an NVIDIA card? I am and had the same exact issue on my desktop. I found a solution in the NVIDIA Control Panel (right-click your desktop and select "NVIDIA Control Panel"). Under "Display" on the left-side menu, select "Adjust desktop color setting". On this screen, click "Use NVIDIA settings". My screen brightened up as soon as I selected this.

The post about the Nvidea control panel sent me down the right path.

I'm setting up a new Acer desktop with Win 7 and Intel integrated graphics.

Rt. click desktop> opened the Intel Graphics and Media control panel > Power tab, Power Plans > changed from "Balanced" to "Maximum Performance" (the other choice is "Battery" -on a desktop machine!).

After that change the 'power saving' dimming has stopped.

Thanks for the helpful clue that led to my solution. This may be just one of several causes for this dimming behavior...

That sounds suspiciously like what happens when the UAC prompt displays. Are you sure there isn't a dialog in the foreground which asks you whether you want to allow an application to perform an action which requires administrative permissions?