My iphone touch screen won't work

Well… My iphone touch screen suddenly stopped working, i didn't drop it or anything. I tried to get it fixed they said that its the touch-screen they changed it and it still didn't work and then they said its the board or something and its still the same. They also restored it and nothing happened. Is there anything else i can do? Btw it second hand phone:/

thanks.

Added (1). How can i clean it?

Added (2). How can i clean it?

Try cleaning it…