As Richard says, dead battery. I had one give up on thePlus8 after 10 years and regular use (50k+ miles). I use a Ctech conditioner and bolt their connector lead onto the battery terminals so a simple plug in to that fly lead. I prefer that to the power socket/cigar lighter method as they can be a bit loose fitting.
A useful additional check is to clean and refit earth connections from the battery to the chassis and to the starter motor.
