The right way!
Using a piece of plastic under the power switch to hold it down means, that the power button is loose. It’s not making a full connection. I used a magnify glass before I used the plastic. I saw the pins go up and down as I hit the button. I placed the plastic as everyone said. I notice it stayed down and it was making the connection to the board. This is a poor design flaw. So I was not happy with the above Gumby fix. It has issues that will get worst over time. So I took my phone apart and added a pin drop of electrical solder to each of the four pins of the on/off switch. You need a very hot soldering iron and the size or diameter of solder I used is .025in/0.64mm. Once you soldering iron is hot, you just need to tap each corner quickly with very little solder on the iron. Make sure you’re in a very well lit area. And to see the connections and pins better I used my magnifying glass and focused on the areas. Anyway my power button works better than before. So I am very happy now. (Do not try this if you don’t know how to solder) you mess it up…