The Mk3 has probably crashed and died.

But check the following:

When the radio is on, can you control it (change stations etc) and see the station names in the display on the dash? If so, radio is fine

When the radio comes on and the ignition is on, can you see a faint glow on the LCD broad monitor screen? If so, the backlight is OK and likely the nav is the problem

The easiest and surest way to tell is to swap the nav with a working unit from another car. Ask on this board for fellow board members living near you to help you

If the Mk3 has dies, the easiest and best thing to do is replace it with a Mk4, much faster and improved graphics, 3D view, and more customisable.