Okay here's your problem: You're not running the latest IE. I got this until I upgraded to the latest IE explorer. It froze like a deer in the headlights and then shot off again like a bullet through the air. Sorry for the strange analogies, but it's a fair analogy of what is happening. Check your IE explorer. Are you running IE6? Have all the latest devices? If this still doesn't help, try returning to a time in your system restore that you remember when your computer worked properly. Otherwise reformat your computer.
I don't use IE.
And yes, I have Norton 2003 on this computer, and Norton Personal Firewall, I want to say 02... I keep getting updates for them. Lost the serial # for my Systemworks 04, so I can't get that back on... but anyway, no, it just happens spontaniously, nothing specific triggers it from what I can tell.