Chosen Solution
My faithful A1278 mid 2012 Macbook Pro 13” finally bit the dust after it took a water bath in my bag. I’ve managed to get it working again but I suspect there maybe a power management issue on the logic board. The Mac boots fine with battery plugged in. However, when I plug in the power adapter nothing. When I unplug the battery and power the Mac with the charger voila it boots again.
Take the computer apart and clean the logic board with <90% isopropyl alcohol. That way it keeps the logic board from corroding even more. You might need a new logic board if it does not work after that. Here’s a guide for taking out the logic board.
