If you get problems powering up after screen swap, locate the 3 battery terminal beneath the metal cover. Refer to the battery replacement guide to see what the terminal looks like. Find the +3.7 volt terminal using a multimeter (From memory, it's the one on the right as you look at it.), and short this terminal briefly to ground. (The metal plate surrounding the home button will do.) Then, plug the phone into a charger, and within seconds you should get your confirmation beep and the screen should show that the phone is charging. Wait a minute or so, and it will boot up. This has worked for me on more than a few occasions. I hope it helps