last week my f900bt had the black screen problem, after booting sd music still plays but screen turns black after splash screen and button lights are off. screen light would come back on once i press the map button but its not as bright as the normal screen light that i use to have (button light also come back on). seems like the main screen light is completely not coming on, but a secondary light that goes on only on navi mode is still working (the secondard dimmed light would go off after about half an hour or so)

any idea how i can fix this problem? thanks