1) the Culprit : ibook g4
2) the Symptoms : a) emitting a knocking sound b) my applications went "limp" -- that is, my cursor worked (there's no freezing), and when I rebooted 3) my screen remains dark -- there is a flicker, and the apple icon is barely visible, black on black, but otherwise : nada.
3) Cure? I assume this is a HD problem -- am I correct?
ETA : I'm going to try resetting PMU button, see if that works...