Touch screen still won't work after replacing lcd and digitize

I dropped my iphone 4 and did quite a bit of damage to the front. The screen was badly cracked but would still turn on but the digitizer wouldn't work. I have since replaced the lcd and digitizer and check many times to make sure it is connect correctly and the lcd works but the screen is not responding to any touches. I have replaced lcds and digitizers before successfully so I don't think it's a connection issue. Does anyone know what the problem might be?

Thanks in advance.