Why is my j7 doing this?

[AC Question]

It automatically shut off an didn't want to come back on an it had 90% charge. wen i plugged on the charger the screen was blinking. I decided to go into recovery mood an a blue screen saying something about an os update must be installed or there will have critical problems with the phone. I put the phone to update an it has been updating from 3pm to so far 9pm an still going. i need help with solving this problem.