How To Get Rid Of A Hacker??

I’ve got a hacker who keeps breaking into my computer through my browser. I use both IE 9.0 and Firefox 4.0. It doesn’t matter – he breaks in through either one. It started with him breaking into my Hotmail account; now he is breaking into websites where I shop, especially Amazon. How do I get rid of this guy??!! I’ve got Norton 360 for security, but that certainly isn’t working. What to do??