details details details...without them how can we possibly respond?
is it charged? are you sure?
is the battery in right?
was it dropped? in water?
when was it working last? what did you do in it since then?
when you say black out does it have to be restarted (you see the animation)?
if not, does it show the lockscreen?
until further details are provided i'm going to have to say that the phone just has a dead battery and needs to be put on the charger. smartphones in general have bad battery life and some tasks can drain them in only a few hours.