I have just purchased the S405. The machine came with Win8, and seeing that I was uncomfortable with the Win8 OS. I decided to do a clean install of the Win7. However after updating all the drivers I noticed that the display seems to be dimmed even when it is maxed out.
When the machine was running on Win 8 everything seems to be fine. I believe this could be the effect of a Win7 driver. Could there be a driver I'm missing ?
The BIOS implementation on the S405 was originally developed with Windows 8 preload in mind, and not with formal support for Windows 7 downgrade or clean installs. (Windows 8 supports 101 levels of screen brightness, while Windows 7 supports only 16) As a result, screen brightness of about 50% of max are likely to be experienced under Windows 7 on this system.
A BIOS update to version 8.05 or later should improve brightness under Windows 7