Have you tried to do a repair on the Local area connection? right click local area connection> repair
If that does not work try this.
Start> run> type cmd
In the prompt type: ipconfig /all that should show you if you have a connection or not, ip address subnet mask, gateway, dns server, if you are connected through a router and have windows and the router to automatically detect settings, alot of those may be the same.
After that try typing: ipconfig /release
Than once it is completed: ipconfig /renew
If that does not work you may have to run Winsock XP Fix
, during the update to SP3 some major settings may have been changed and what winsock fix does is it can "cure a lost connection". It will also check for LSP errors.
Hope this helps