No backlight on NAV SCREEN

[skrewcop]

Hi i just took out and disconected my nav unit because i wanted to clean the contacts due to loss of color and fuzzy screen sometimes. Now when i plugged all connectors back in, the display is dark but all the controls on the unit work just fine and the buttons are lit too. If i shine a light on the display i cas vaguely see all the info on it like "settings, board computer, telephone etc..". Is there something i'm missing. Is there some kind of light sensor that i need to check. I would greately appreciate the help as tomorow i have someone who's coming to buy my suv and i'm sure he will change his mind. Thanks
It's a BMW X5 e53 4.4i 2005