I had the same problem with my early 2014 MacBook Air. I opened it and saw fresh milk! My 2-year old had been watching Tinga Tinga Tales on it and must have decided that it was a good idea to pour milk down the keyboard ;-{ In such a case, there is only one thing to do, the distilled water trick. You take out the battery. Then you put your Mac on a baking tray and rinse it with distilled water - humidity doesn't kill a computer, it's the salts, sugars and acids that does (or in this case milk). I repeated five time, submerging the mac every time, then drain and put in the oven at 40 C for 4 hours. Plug back in the battery, and it's as good as new! I'm writing on now :)
