Subaru Impreza RX 2.0 Engine Stop & Start Button Constantly on Green Won't Start

As the title says 

as soon as the battery is connected to the car the dash lights come on & the engine push start / stop button is constantly illuminated green 

as if the car is always ready to be started 

I'm new to owning a Subaru but my guess is that this light should not be illuminated green until I've actually pressed it 

any ideas why it's illuminated green as the car will not crank at all but shows there is power to the vehicle with all the lights etc still working...