Why don't Logitech keyboards' media keys work?

Solution found on this Logitech forum's thread: G510, Media Keys and Windows 8

It looks like one of the first updates messes up the HID (Human Interface Device) service activation. In order to fix it, follow these steps:

1. Press Windows+X and select "Computer management".
2. At the left, under "computer management", you find "Services and Applications". Open it and select "Services".
3. Search for a service named Human Interface Device Access (or something VERY similiar).
4. Once found, check the status. If the value is not "Started", start it.
5. To make sure it will be on also in the future, check the Startup Type value. If not "Automatic", right click it, and select properties.
6. Under the tab "General", change the Startup type to Automatic.
7. Apply and close.