Just had the same issue. Phone is 1 year old, I put it to charge with battery at 10%. When I picked it up a bit later, it was not responding at all, also not charging. Led was still blinking green once in a while. Tried multiple tricks.. eventually I managed to get it started again following video on YouTube: 'How to fix Xperia Z3 won't turn on' by David Novak. After 'press volume up and power' phone vibrated 3 times.. Then powered up. Showed a sort of 'work in progress' sign for a while, then rebooted!
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