Is the problem confined to IE only? Have you tried another browser like Firefox, for instance? Are you able to send/receive email? Is your Internet connection itself failing?
Using their search facility (click here) this is what I could find that may relate to your problem:
1. Cannot access the Internet
- NIS 2005 & later click here
- NIS 2004 & earlier click here.
2. Problem with *specific* websites click here & click here.
3. Problem with *secure* websites - click here.
4. "Internet Explorer cannot access the Internet when Norton Internet Security 2006 and a non-Symantec firewall is installed" - click here.
Hope this helps. G