Can you give a bit more information?

Its silly but sometimes you have to check if ure power adapter is functioning correctly (or even plugged in).

when was the last time you booted normally and how did you shutdown? Did you install any programs before this event happened?

And like Raxi said, try pressing the power button for a bit longer.

Unfortunately if yours is a hardware problem there is very little you can do about it. But if its a software problem then chances of it getting fixed are higher.

Peace.