Yes! Thank you Josh! I just replaced the screen assembly (frame, screen and digitizer in one piece) on my Nexus 4 and the phone showed as charging when plugged in but wouldn't turn on.
On the new frame the two small gold plated prongs on the power button piece were not touching the motherboard, when I pressed them to the motherboard and pressed the power button the phone turned on! Now I have to find out how to get them to touch all the time but at least I know what the problem is.