Have you looked at the switch that tells the Mac when the lid is closed? That's often a reed switch and magnet. Reed switches have a tendency over time to get "sticky", and your 1400 may not know the lid is open, or it may be getting conflicting signals. You can sometimes unstick a switch by tapping in the vicinity or waving a magnet of opposite polarity near it. I don't know what kind of switch the 1400 uses, but a sticky switch certainly messed up my Wallstreet.