Update = After verifying ownership and completing troubleshooting, a DELL-Cares agent setup a like for like system exchange.
I recently purchased a Dell 7750.  According to this article: [URL] Switchable graphics must be enabled to permit brightness changes in BIOS.  The article states: The internal LCD brightness on these computers cannot be adjusted outside of the operating system (OS) when switchable graphics are disabled. This is using either the brightness sliders for battery or AC-power, or the keyboard shortcut in the BIOS methods. However, both methods work as intended when the switchable graphics are enabled or you are in the OS. The problem is that I have switchable graphics enabled and the brightness sliders still do not work in BIOS.  Once the computer boots into Windows 10, I can control the screen brightness either via the function keys, Windows settings, or the Intel settings. Strange thing is that I have the same BIOS setup on my 7740 (switchable graphics enabled) and the slider controls in BIOS work perfectly.  Any ideas how to fix this?  Thanks. 
Dell 7750 Screen Brightness