Chosen Solution
Often I would have to keep pressing the start button because the system would shut down during startup. Eventually it would start, but now it’s dead. I’ve replaced the battery and the MagSafe charger indicates Green
OK now that we’ve narrowed down your system. Your issue is a bad C7771 capacitor which Louis goes over here in this video: What causes no power most 2008-2009 17" Unibody Macbook Pros & how to fix it This is a tricky soldering job! I would find someone with the proper skills and tools to properly diagnose it and if bad replace it.
