We'll need a bit more information in order to answer that. Some things that might help to know:
* What happened before the problem (shut down when using, ran out of power, dropped, has it ever got wet, or did it go on charge normally and just not wake in the morning)?
* Have there been any other problems previously (crashes, overheating,...)?
* What is the current state? Will it not turn on at all, or does it not boot completely (which some people have called "not turning on" when posting questions here)? If the screen comes on at all, what happens?
* What happens if you plug it in to a charger? Does it start to charge or not?
Try removing the battery for a minute or two and see whether it's any better. If not, please post again with the most complete description you can give.
Thanks, and good luck.