Why is my phone not turing on?

first my phone died and than i kept in on the charger it wont work i tired to press the vol up and the power button and i also tired the vol. down and the power button nothing would work every time i press the vol. up or vol. down button it gives me the os and i pressed the vol. up to down lode and i also tried to press vo. down nothing would work it stays shut . what should i do ? HELP ME PLZ