I have a similar situation.
I replaced my screen and after putting it 80% back together I wanted to test the digitizer and noticed there was a 1-2inch vertical black strip almost center of the screen.
So when it powers on, only the right half of the apple shows and when the home screen loads there is the black bar going down the middle.
I tried reseating the ribbon cable but I'm not sure what I'm doing wrong because I'm still getting the same bar.
Should I press harder on the ribbon cable? Did the LCD go bad?
The directions I followed left the battery connected, but I ended up disconnecting the battery (AFTER I disconnected the LCD) so I hope I didnt mess anything up by doing that.
Please let me know how to test, and what to check. Thanks