Why the screen is black?

Hi!

I have a problem with my iPhone 5C. I was using my iPhone normaly and i decided to make a little darknes my display, so when i was moving the control of brightness it happens blackout! I restarted my phone many times, even using DFU mode. The problem is that the screen is totaly black and it is without any respond (touch panel also dosen't work). You hear the sounds of Siri, soud of clicking the buttons, but nothing on the screen - ofcourse i replaced the lcd and it is the same. Many times i checed the connectors, but still no solutions. Any ideas?