Why my power button will not turn my power button off

[AC Question]

When i cut my phone on it just stay on the screen that say samsung galaxy mega gt 19200 and it just be blink it over and over with a noise

 

[B. Diddy]

Welcome to Android Central! Do you mean it starts up, you see the welcome screen, then it shuts off and then powers on again by itself, in an endless loop? That might be a failing battery. Try a new one.