Q: iphone 5s new touch stop to work

Hello,

i'm sorry for my bad english, i'll try to write it in a right way:
The touch of my iphone 5s twice-three in a day stop to work.When it does that I hit the screen right on the bottom part ( where is the clock on display) with 2 fingers and it restart to work.
How is it possible?

I've changed the touch, it has the same problem.... i think that is an hardware problem....but which one?

Thank you to everyone,

Marta