Default [Q] galaxy s2 black screen problem

my galaxy s2 has a strange problem , as i turn it on , it has sound and even can connect to computer , the 2 soft button down on the sides turn on but the screen is black and dead , nothing comes up . i replaced the lcd screen but its the same problem , can anyone here knows what could be the cause of it and how to fix it ? i tried even to flash rom via odin which pass but same problem with the dead screen