Are your AC adapters all 65-watt? 15" PowerBooks will not even power on with 45W AC adapters.
Is the behavior with the new DC-in exactly the same as it was with the previous DC-in, or is it behaving differently? Do you know for sure that the new DC-in is good, and did you buy it from somewhere that is guaranteeing it and will swap it out?
I would remove the battery, connect the AC, and try to reset the PMU by holding the power button in for 10 seconds until you (hopefully) hear a tone and see the sleep light blink.
Assuming the power adapters are good, and the memory is good and firmly seated, I really can't think of anything it could be besides the DC-in or the logic board itself. Again assuming the AC adapters are good and 65W, it is odd that you don't get a light on the DC-in, and that may indicate that the DC-in connections to the logic board are not in place or fully seated.
If that's not the problem, I would swap the DC-in for a known-good one and try again, and also test your AC adapters on another machine so that you know for sure they are working. I know that sounds silly, but when troubleshooting it's 100% critical to know for sure that components are working, and making assumptions, no matter how good they seem to be, always causes problems. (For instance, maybe your computer or a flaky power source blew out your AC adapters, and now that you have a good DC-in, all the adapters are non-functional so the computer just appears to be bad? An unlikely scenario, but you see what I mean....)