Can you do this;
- Download and install Wireshark from
http://www.wireshark.org/download.html
- Give a restart and dont open the browser.
- Disable all internet based services (Automatic Update, Downloaders and all other stuff)
- Run Wireshark and select your Dialup / Ethernet connection and set the filter as "HTTP"
- See whether there is a lot of traffic going in/out of your pc.
Check what are the URLs that the packets are going / coming from.
This way, you can make sure there isn't any trojans / worms running in the background eating the internet connection and processor.
Cross check the addresses/IPs with blocked sites and who.is to see who owns them.