black screen after screen replacement connects to itunes

hi i replaced both LCD and digitiser but the screen remains black no back light or visual when i plug it in to itunes you can hear the bleeping sounds working fine and the ipod loads up correctly in itunes but still not visual i have tried usual fixes checking cables are connected correctly and using different lcd's. i have also tried restoring the phone and loading it in recovery mode by shorting the battery but nothing seems to work. the phone is now on, charging and connected to itunes and has been restores and is running IOS 5.1.1

any help would be great thanks