Problems accessing certain webpages

I'm running XP Home/SP2 and recently installed Norton Internet Security 2005. Since then I have to have it disabled most of the time because it won't let me access certain sites (for instance - Amazon). However, even when disabled, I struggle to access certain sites (particularly banking sites). My ISP is AOL... and with many sites I can access through AOL browser (which I don't want to use), but not IE, Mozilla or Opera.

I uninstalled Norton, but my computer still had some issues with certain sites... so I re-installed it.

Before I installed Norton in the first place, I didn't have any problems at all. I've checked the settings in the software and in the browers, and can't see anything obvious that I need to turn on/off.

It's just annoying, needing to fight for every download. On one banking site I have to log onto my work network from home via a VPN and access the internet from there.... is it Norton ? Is it AOL ? Is it something else ?

Any help gratefully received