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.