Powerbook G4 won't turn on AT ALL

Question

So I have a PowerBook G4 that hasn't started up in about a year. When I press the power button, nothing happens. With the power adaptor plugged in and the battery removed, the light is amber, not green. I've tried two different adaptors, both do the same thing.
I've recently tried to diagnose the problem and everything I have found online leads to two possible problems:
1. The DC / Sound Board
2. The logic board
I ordered a new DC board that came in the mail a couple of days ago and the exact same problem is happening. Light on the power adaptor is amber, powerbook won't turn on. This time, however, I noticed the battery started charging when I put it in.
Is there anything else I can check to see why it won't be starting? I've already tried resetting the PMU. I've unplugged the backup battery. I've unplugged the hard drive, the dvd drive, etc etc... The only thing left I can think of is the cable connecting the keyboard to the logic board. How can I test that? I can't figure out how to turn on the computer without this plugged in.
Anyway, this might of course be the logic board, but I don't want to pay to replace it if that's not the problem. Is there a way to check the logic board and test if that is in good condition??
Yikes, sorry about all the questions.

Answer 1

Is there a way to check the logic board and test if that is in good condition??
Yes, if you have the original OS X disks that came with the system, so when it DOES turn on, you can insert the first one, that says AHT Version x.x on the gray disk face, in small print, hold the alt key, choose the Apple hardware test,d and when prompted choose the extended test. However, that of course assumes you can power up the system.
The power circuit only has 4, well maybe 4.5 components .... power adapter, battery, DC-in card, logic board, and some would argue the PRAM battery. By process of elimination, it would point to your logic board, although some would argue you need a working PRAM battery to start the system, which I'm not entirely sure about. However, it's possible there is an issue with the cable attaching the keyboard to the logic board. It's not unusual for it to be tricky to get the cable lined up and inserted correctly into the socket. That cable doesn't have a reputation for breaking or going bad, however.
At this point, you're into substituting parts until the works. You don't say where you're located, however, if you're in the US, you could take it to your local Apple store, and ask them to send it to the Apple Depot for repair. If the case is in good order, it should cost around $350 for them to replace whatever needs replacing to get it into almost new condition. If the case is banged up the price goes up another $300, give or take. That's much cheaper than having them do a repair in the store, which would be ~$750 just for the logic board.