Most common cause of failure is blown thermal SMT fuses on the Powerbook 2400c - resulting in the "green light of death", over time. There are several thermal fuses on the motheboard that can can fail, I recall mine had 2 out of 4 that needed replacement, and I had to do it again when I used an original Apple Duo charger on it once (DON"T use, just use a charger designed for a Powerbook G3).