Unbelievably simple, once I found it. /etc/hosts had lost several lines. I have no idea how that could have happened, but one of the missing lines was the address of the server. I can now see all the server's shares within konqueror!
Thanks for all the help. It was starting reading the howto that made me realise that checking that file would be sensible. I would never have thought of that. Another lesson learned :-)
Anne