I just replaced the battery, now the display doesn't work
I just used your step by step instructions to replace my battery. I have sound, but the screen remains black. I have rechecked the connections and they appear to be fine.
What can I do to fix this?
First step is Reset, hold together the Home and Power buttons for about 15 seconds, the iPhone will restart. See if it is fixed.
If not, the usual second step is to make sure Flex Cable #1 (LCD display flex) is seated on logic board correctly. You say you have done this.
Try first step, if not working consider second step.