Did you try to long press the power + volume up/down combo if it still boots up?
You can thoroughly read this which can greatly help you:
I really hope that your phone will return to life again.
Yes..I happened to flash my phone again..at 4% battery remaining LOL..!! I dont know how that happen however i just wanted to make my phone run again..in the morning i connected my phone and started flash tool..loaded the 4.4.2 and WOOOP!! It went ahead and flashed the mobile..THANK YOU ALL GUYS FOR REPLYING ME AND HELPING ME..!! REALLY APPRICIATED..!!