Stupid question but where are you inserting the disk?

The CD player behind the nav screen is just that - an audio CD player (unlike many vehicle nav systems) - do you have a nav computer in the boot behind the flap?

Some vehicles have just TV and OBC - no Nav - depends on the ordered options, though if that is the case, it should be easy to retro-fit a Mk3 or Mk4.

If you DO have a nav computer in the boot, then it looks like there is a problem with it as even without a map disk you should get a request to load the map disk on the monitor, and in the menu there should be a navigation option.

Can you confirm what you have in the boot, and where you have been trying to load the OS and nav CD?

Cheers