I think I'm having the same problem: after I soldered a new usb socket into the phone with wires to the pads. Mine is very far behind the hole of the housing, that's why maybe it doesn't get connected properly. The other possibility may be a wrong connection, I'm not that sure with that GND-pad.
I didn't had the time yet to open it again. Maybe you can just compare your connections with those in the service manual or from the forum.