Update - swapped to 4:3 screen up front to test - still the same - black screen

Have tried endless nav software updates (different versions V17, V18, V24, V25) red led on and off as disc gets read but still nothing happens on screen.

Last time this happened I did get the os to reload and saw the screen updating but not this time.

Do i conclude the nav computer needs changing then? Or does anyone know of how to test/repair the computer.

Help appreciated.