Thanks for this tip. My Sony Aqua died suddenly, so I googled and found your advice. I did this, and held the buttons down until the android kicked twice and showed a red light. It then started to charge, and showed a green light. No good if you are stuck in the middle of nowhere and need an emergency phone, of course.
Also had a sudden death while not using the phone and with around 75% charge left.
Tried every tip and trick know to mankind but it kept silent. Then i red about a "new" trick. I will discribe it as best as i can.
first hold the volume down key in for about 30 seconds. After that try to hold down the power and volume up key until you feel three short vibrations. Let go of the keys and immediatley plug in the micro usb power. This can work but it didn`t do the trick for me. I did it slightley different. I kept holding down the power and volume key and kept holding it down while at the same time plugging the micro usb in. I got a constant blue led and when i pushed the power button the z3 started to charge. when it was full i hit the power button again and YES! it came alive.