Why does my phone turn on only while charging

so since I have updated the phone to 5.1 UI it started to flash green in the bottom while charging and the screen off. And it doesnt turn on by the power button only when charged this happened for the first time while the power is 15% it doesnt want to turn on but I can feel responsive vibrations but the screen is just black but when I charge it it turns on the screen with higher battery percentage.