Ok on the software thing normally something newly installed may cause a problem on odd occasions, so since that is cleared up that knocks one possibility out.Since you mentioned you have no other Security Software apart from Windows Firewall and you did temporarily disable that to see if the internet worked (which you said it didn't), so that knocks out another possibility The Database Date should be 8/6/2009 (British Date) or 6/8/2009 (American Date) as it is shown on the program, the Database Version should be 2249. But since you can't connect to the Internet with any other program I guess we can't update it but it should be ok it's barely 2 weeks out of date so there shouldn't be much difference between the versions, try running a scan and post it in your next reply.Since you mention this quoted below, I guess we'll look into that more now the software side seems to be ruled out
Other than that, I've noticed in the "Network Connections" box, there are only two icons - "1394 Connection" and "Local Area Connection" whereas I used to have three. The last icon called "Internet Gateway". How can I remedy this?
Try following this article which tells you how to create a new network connection - http://compnetworking.about.com/od/windowsxpnetworking/ss/windows-xp-network-connections.htm, hopefully this should help creating the new connection to your Router. It's odd that you can connect to the internet with Opera but you say that "Internet Gateway" which you used before has gone, but Opera is still working, How are you connected to your Router now Wireless or Wired?