What kind of internet connection do you have?

If you have broadband, do you connect directly to the modem or through a router?

Is it just your web browser that can't access the 'Net, or do you have no Internet access at all? The firewall component of Norton Internet Security gets "confused" sometimes, blocking some or all legitimate network traffic.

First- try uninstalling the entire Norton package and reinstalling it. If that doesn't work, this topic on Symantec's support site pretty much covers the possible causes and remedies for the problem.