I have a new MacBook Air which keeps turning off by itself and now won't turn on at all...

It's been working fine since I've had it but yesterday it kept turning off by itself and then within minutes off turning it back on it would do it again. Also the little box kept popping up asking if I wanted to sleep, restart etc as if I had pressed the power button. I tried to turn it off completely and now it won't turn back on at all. If I plug the charger in the green light comes on but nothing happens on the actual MacBook itself. What do i do ?