Handy doesn´t react by pressing on/off- Button, just blue light

I turned my Handy into Standby and after 2h, i tried to start it. But all i got was a Blackscreen and the blue light in the left corner thats lights on when i press the on/off-Button. And when i try it to charge, the blue-light lights all the time. What happend ?? Waht can i do to fix it ??