Your Nav Computer has 'dropped off' the i-bus and is not responding. The TV Module has taken over driving the graphics/menu's.

Suggest pulling the Nav fuses (look in your owners guide or the fuse decal plate in the fusebox) - leave for 10 mins and re-insert. Failing that, try disconnecting the battery, though be prepared for some odd warning lights when you re-connect (which should go away after a couple of minutes driving).

Also check your battery voltage as this can cause issues with the Nav computer.

Before you do anything though, ensure the red led on the nav computer isn't flashing...