This happens on my BT home hub sometimes..............this has a little pin hole and I shove my pen in it and it resets the router to the default settings which seems to do the trick.
Switch the router off then on again to reset it. There should be no need to return to the default settings, especially if you have changed the password!
Craft, I'm not with BT, but my router sometimes doesn't pick up the internet connection althouth all the DSL and wireless lights are on. A simple switch off and on always does the trick. I changed the encryption code a few years ago, which is set on all my 3 PC's, therefore a 'factory reset' would mean changing either the PC's or the router coding each time.