I've got Powerbook G4 12", that works normally with the external screen - but inner screen shows nothing. Inner screen is checked - and fully working. Powerbook starts, chimes, then screen flickers a bit - but stays black. I though, that it's hall effect sensor - but I checked it, DC-DC Board - everything works fine.

Suddenly I checked system properties - and found out, that it thinks that notebook is closed.

Also I found out, that inner keyboard worked fine, but is not working anymore - with screen at once. Keyboard is 100% working - I checked it on the other logic board.

I already compared this logic board with working one - but found nothing. I think that some single little part is shorted or out of order - but I can't find anything. What is needed to be checked first?