I does sound like the MBD, they are not hard to change. Less than 1/2 an hour if you have done one before. It sounds like the DC socket is loose, which is part of the MBD. What lights come on when you try to boot ? Does it turn off by itself ? Have you reseated the memory ? It could also be bad memeory, are you able to swap it ? If it has 2 sticks, you can try combinations.
You will need to take out more than the KBD. Dont rule out a memory reseat, many machines have come back to life after a reseat.