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There was some milk spilled on my Macbook air (actually on the keyboard) . I shut down it immediately and found someone to dry it for me. Now all the things are going well on my mac except that there is no light on magsafe + no charge. what should I do ? did the milk damage the motherboard?

Yeah, there is an issue with something called the onewire circuit inside the motherboard, which is responsible for the green light showing up. This is most likely because a crucial voltage rail called PP3V42_G3H has been short circuited due to corrosion from the milk, and you can get it fixed with motherboard repair