Mr C, you said:
As both things happened at the same time I am assuming that they are linked.
Is it too late to remember what it was you did just before these two events happened?
To ping and not to Browse,
that is a question.
Try "ipconfig" in a Command Window and see what the IP address is of the recalcitrant machine. If its not in the range that your Router would like it to be, it is likely that Boy1's Winsock is broken. I assume that your Router expects all Machines to do what they are told and if they don't it will not play ball.
This has got me out of a hole more than once. WinsockFix can be found on may sites; it has become very popular.