Ward

I've just bought a 2015-2016 disc from ebay to update the 2007 disc in my car. When I changed it, it said an update was required which would take 20 minutes - and had the option to continue. As I was late, I switched the car off thinking I'd do it later. Starting the car later - the satnav button on the home screen just beeps - no satnav, and no message. I put the 2007 disc back in - same thing. It obviously wants this update, but I've got no idea how to re-boot it ! Can anyone help ?