Backlight works, but no LCD or digitizer.

Hey! I just followed the guide on how to replace the LCD Screen on my 3GS (the old screen worked, but had no backlight, the new screen worked perfectly, it was tested beforehand), but after I finished the repair, The screen no longer works. Only the backlight lights up. The phone itself connects to a PC, and is detected, but the LCD and digitizer stopped working. I tested the old screen, and now that didn't display anything either. I already tried restarting the phone, but that didn't fix it. Any idea what the issue might be? Thanks!