My power button was no longer working.
I debated also replacing the power cable as recommended but decided to replace only the button just so I could isolate what the problem was. Replacing the button fixed the problem. Hard to believe that replacing that little piece fixed it, but it did. I didn't reconnect the Wifi antenna carefully, so my Wifi and Bluetooth were not working. I had to disassemble the whole thing again, but the second time was much easier and now it's working.
I highly recommend the anti-static project tray. It is critical to keeping track of all the small parts. Also, starting the standoff screws with the Philips screwdriver makes them easier to start. Then tighten them with the flat head.