Pismo PowerBook not starting up

I have a Pismo Powerbook (400 MHz upgraded to 500 MHz, 384 Mb RAM, 12 Gb HD, Mac OS X 10.4.11) that I purchased on Ebay 2,years ago. It was working fine but now it wouldn't start up. I replaced another working hard drive and processor and still no go. When I pressed the power botton, there was no chime but the keyboard does light up when I press the caps or number key. I checked PRAM and seating of hard drive and processor and connections, they all seemed fine. The battery is fully charged and the machine wouldn't respond with power adaptor connected either. Does this sound like a logic board problem? Is there a way for me to check? If it is the board, do you recommend a person without prior experience to replace it following your manual given the number of steps involved? Although the laptop has outlasted its time, it is still a real classic that I intend keep. I can still surf the net, do some email, word processing, music, photos, and even watch some movies. Any useful suggestions are very much appreciated.