Why does my iphone 4s keep switching on and off?

So i dropped my phone, like anyone does, and I was listening to music, and the screen and everything worked fine, everything is fine, no cracks, no nothing. Then I tried to lock the screen like everyone does to save battery, but it lagged when I used the button, and me being impatient used assistive touch as well, i guess the speed of locking the screen merged and the whole screen just had black lined stripes, like those of a old television set with white static. Now, it does the whole shutdown sequence and start up sequence over and over, and I can't hold the button down to stop it, or turn it on. Eventually I left the thing to keep shutting itself on and off. And it ended up working but when I used the button it does it all over. What do i do?

1] FLASH your MOBILE OR

2] CHECK FOR ANY HARDWARE FAULT IN SERVICE CENTER.

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