turn off your firewall and see if it works...also try to reinstall the browser
uninstall any programs like HotSpot Shield,Expat Shield,etc.
i Didn't Use Dynamic Ip!Your using dynamic IP Bacs? a friend of mine has same problem as you and he uses dynamic IP.
go to your network connection and right click > properties > and remove QOS service > apply changes and then restart your PC
here's an example:
http://img651.imageshack.us/img651/6862/unledrcp.jpg
http://img831.imageshack.us/img831/3456/captureua.jpg
Try to find a solution with your net providerFor assistance, contact your network support team