iPhone 4s dropped-now the screen is black
It sounds as if it may be a simple case of the cable connecting the screen coming loose - the fact that the digitizer works could indicate that the cable isn't seated correctly - i.e. some of the connections are being made but not all of them. You say that you replaced the screen yourself, so I assume you're fairly competent at taking it apart again... If so, try doing this, removing the cable connecting the screen, and then reseating it.

Alternatively, it could be that the impact has broken the part of the screen required to display things, in which case, I'm afraid you're looking at replacing it again!