Why aren’t my media keys working?
The media controls are only available when using the USB connection on your keyboard, so both connections need to be plugged in to your computer. If you are using a Das Keyboard with a Mac you have to hold the Fn key while pressing the corresponding media key (in blue) in order for those functions to work. Many web-based programs don't support all media controls. If they don't work in a computer-based software such as iTunes please check for any updates to your computer and try the keyboard on a different computer to see if it has the same behavior.
The brightness controls will only work with an Apple monitor because most PC monitors don't support brightness control from a keyboard. A Bluetooth keyboard connected to your Apple computer may also interfere with the brightness controls.