Digitizer not working even after replacement.

Hi basically got a 2nd hand iphone 4 with cracked screen and unresponsive digitizer.

Was told that it was dropped and thats all the info i have on the phone.

So i have fitted a new front screen assembly to the phone and the digitizer still doesnt work!

I have successfully replaced 3 different digitizers on the iphone 4 in the past and am pretty confident its nothing i have done during the repair, The phone hasnt previously seen water as the white water stickers are still clean and white.

Not sure what to do now so figured i would ask on here and see if any of you guys have some advice, thanks.