Check your hardware (cable, modem, connection, etc.) Make sure that nothing here is loose or possibly faulty, ping your provider or a known website (click Start button, click run, type in cmd, type in ping "hostname" [do not use the quotes when typing the hostname], a simple ping would look like this "ping www.altavista.com" without the quotes.
After that run a traceroute, same as above but instead of typing ping you will type "tracert" which would look like "tracert www.altavista.com" without the quotes.
This will tell you if there is any interferance between you and a website, if there is check the hardware your connected through then call your ISP.
