@ramenzack I think we just at least give you some things that you can /should check, to see which way you are going with this. Use these guides to work on your MacBook [[Topic:MacBook Unibody Model A1278]]
I suggest that you follow the Apple flowchart on how to test for the No Power Issues. After all, even an issue with the DC-In Board could be causing your symptoms. Check the Functional Overview and you see which part could be the culprit
[image|2998728]
Here is what Apple recommends to check:
[image|2998730]
[image|2998733]
[image|2998732]
Do a close inspection of your DC-in board and your logic board. Check for anything that looks odd. You can always post images of what you see, or need to know more about, with your Question. [guide|21499] Let us know what you find out with all of this.
Also, you said that "that the battery already was tested." but did not tell us how you tested it. A bad battery may still show some voltage but breaks down when power requirements are needed. Do not assume it is good.
Even if everything should fail, you can still replace the logic board from reliable sources, for a fraction of the cost of a new computer. It ain't dead until you say it is.
Repair is War on Entropy!