Chosen Solution
(My English conversation is really really really bad. I’m sorry.) A few weeks ago, I opened my macbook; problem is CPU temperature and cooling solution. My conclusion is simple maybe - paste new thermal paste and get rid of all dusts inside macbook. So, I saw macbook disassembly in this site and follow the steps and reassemble it. Assemble might be perfect, but power button not working :-( But, connect power cable, macbook boot automatically, saw apple logo. Shut it down and connect power cable again, but none of the work. Power charging works good, battery check button also works good, but power button. What is worng?
I’m suspecting you didn’t get the ribbon cable from the keyboard seated fully review Step11 in this guide: MacBook Pro 13" Unibody Mid 2012 Logic Board Replacement, I use some electricians tape to create a pull to help in holding the cable in place as I latch the latch. Also make sure you haven’t torn the cable as that can also effect things. Disconnect the battery and re-attach the MagSafe charger the system should spontaneously start, if not you have to go back into the system and review what you did as something was forgotten or damaged.
Try taking it apart and try the power button while it’s apart. If the power button is working when it’s taken apart then it’s an assembly connection issue. So check the cables connectors and flex ribbons to make sure all connections are connected and not tweak on the side. I’m trying to picture it in my head how you took it apart, however since you did to clean the DUST from the insides. There shouldn’t be an issue with the power button. Thanks hope this helps
