Other people have had this problem Fergie. This google.groups thread: How do I solve the "404 not found nginx" error? suggests that something has modified your hosts file (possible Qhosts trojan).

There are instructions for removing the offending lines from the hosts file in that thread (if you're using windows). Run your AV software if you've got some, if not try one of the online scanners; fixing the hosts file may not remove the cause if you've got some malware.

Mick