GPS system does not know where it is. Mercedes 2004 E-320 Wagon

GPS system does not know where it is. The unit appears to be Mercedes OEM equipment, matching the appearance of the units I find in advertising photos and on Amazon. There was no navigation CD with the car when I bought it in Apr 2016. I got what claims to be a 2006 Mercedes navigation CD through the internet. It worked until Jan 2017, first insisting that the car is parked in the middle of Lake Michigan while I live near Minneapolis, MN, and showing a correct instruction from there to my destinations in Minnesota and the Dakotas. Now I only get a white screen.

The factory service manual tells me that I need to insert the navigation CD into a unit in the trunk on a sedan, but says nothing about wagons, removing the CD or leaving it in for operation. The manual has great detail about operating the system from the driver's seat, but nothing further about the hardware. I don't find a CD reader hidden in the rear of my wagon. Since my car has a 6 disk CD changer in the dash, and a one disk CD player slot on the entertainment unit I have been inserting the navigation CD into the single slot.

Am I using the correct CD player slot to load the navigation disk? Do the CD's expire? Must the CD be in the unit drive to work, or does the unit download the data to memory allowing the CD to be removed? How do I reset the audio/navigation system to clear bad settings or data? Am I on the right track, or is it just broke?