Function Keys Display

I recently had to reinstall windows on my XPS 15 (l521x) and i now have the F-keys working with their assaigned function (Brightness, play/pause, volume, etc) however, the graphic overlays no longer appear.

For example  - Fn + Brightness^ - will increase brightness but with no graphic showing what the current brightness level is.

Any way to get this useful feature back? 

Thanks in advance.

Lewis