Oh ouch. If connecting to an external monitor didn't work, things could either be very bad, or not so much. If no external monitor is working, it usually means that your graphics card some how got messed up, instead of you actually breaking your LCD screen.
I'm pretty sure the graphics card is soldered on for your laptop, so while you don't want to take everything out, you might try lifting up the top of your case, [http://www.ifixit.com/Guide/Repair/Installing-PowerBook-G4-Aluminum-15-Inch-1-1-5-GHz-Heat-Sink/237/1|following this guide], and see if anything is out of place or disconnected.