if you are using an external keyboard and mouse, try to go into clamshell mode, boot it w/ the screen open, and once it has booted,close it, then wake it up w/ an external keyboard and mouse. it will display ONLY on the external screen. then open the powerbook so you don't melt the keyboard, and use it that way. this works fine on my macbook (even though it has a good screen, i tried it once) but this will render the internal keyboard/trackpad useless while it is in this mode.

anyway, good luck!

P.S. the powerbook should work just fine w/ the inverter and screen cables disconnected from the lobo, it did on my pile-of-parts PB 16 inch