I can't diagnose this problem from a distance, but I can suggest a few tests that will help you help yourself.
First, check some other Web sites. There's no reason to worry about access to the entire Internet if only one site is down.
Next, try changing your DNS server. See Speed Up Your Internet Connection by Changing Your Domain Name System Server for details.
No luck? Now it's time to determine if the problem is with your computer or your Internet connection. When the Internet goes down, try another computer--or some other device in your home that uses your network to access the Internet, such as a smartphone with G3 turned off or a tablet. Can they access the Internet?
If your PC really is the only Internet-capable device in your home, borrow a laptop or tablet (an iPad Touch will do), or invite a friend with one of these over.
Whether or not the problem occurs on a second computer, you need to determine if the problem is with your Internet connection or your local network. Try to access something else on your local network--a network printer, or shared files on another computer.
If your PC can't access anything on the local network, but other devices on the network can access the Internet, try these tests:
- Turn off your firewall. If this solves the problem, examine the firewall's settings or replace it with another one.
- Check the connection. If you're using ethernet, replace the cable. If you're using WiFi, try ethernet. Or change the location of your PC to get a better signal. Make sure you have the right security password.
- Uninstall and reinstall your network adapter drivers.
If the problem is limited to the Internet, but happens with every device, replace the cable connecting the modem to the router. If that doesn't work, replace the cable going from the wall to the router. If none of these help, complain to your ISP.
Finally, if none of your computers (or other devices) can't access the Internet or your local network, the problem is probably with your router.
