This is a screw up with the BT installation itself. How am I so confident? Guess where I just got back from! The whole problem revolves around the WEP wireless key, which is printed on the back surface of the BT router. There are two in fact. One for BT home hub and one for BT Fusion. The key is difficult to input into the PC so that you can log on and I am finding the same difficulty, though a few days ago, when faced with similar trauma, I spoke to the BT help line and we got it sorted on another desktop machine. Thing is, I can't remember exactly how we had to fiddle it, so sleep tonight and a quick call to BT will have both you and me sorted in the morning.
Conan's top tip for Sunday - Never volunteer to help friends
Conan