Setup: PowerBook G4/667, OS X

Problem: My PowerBook generally is not starting up at all (i.e. you press the Power button and nothing happens). Occasionally you do hear a clicking/whurring noise. Less occasionally you hear the startup tone. In both cases nothing else happens.

Other Pertinent Info: I don't have another 65W power cord available, but I do have a 45W one. (I tried it; it didn't help). When the Power cord is plugged in, the green light on the power cord lights up. The battery has some (not a lot of juice). Before, when I ran the computer off of the battery, after a couple of minutes I get the warning that the battery is low, but nevertheless, I could run the computer for about a half hour on the battery. Currently, all four lights on the battery light up. When I press the power button, though nothing happens, the Caps Lock light does go on when pressed.

Things that I have done: I've reset the PMU (as instructed on the Apple Tech Doc-i.e. pressed the reset button on the back where the ports are, waited 5-10 seconds, then pressed the power button). I also did this after the battery was out and the computer was unplugged for about 10/15 minutes. At one point I took out the hard drive (to temporarily put in an enclosure so I can copy some important files that I need to work on). With the hard drive out and just the battery in, (after the 50th/100th time) I tried to start the computer again and it actually started with no problem. (There was no hard drive, thus the flashing ?, but it did start). I have not been able to reproduce that, though.

Where do I go from here? I am the technical type (I've taken apart most of my PowerBooks at some point) so I am capable of more complicated procedures (though would prefer to avoid them if possible).