If your computer connects directly to your cable modem, it's most likely that you're supposed to be getting all of your IP info from your service provider automatically via the DHCP protocol.
Open your Network Connections, right-click on the Local Area Connection, and choose Properties from the resulting menu.
In the General tab of the Properties window, double-click on the "Internet Protocol (TCP/IP)" entry. Check the "obtain...automatically" options for both the IP and DNS settings.
Click OK in the Properties window and again in the Network Connections window.
Open your Internet Options control panel. Go to the Connections tab and click the "LAN Settings..." button; make sure the "automatically detect settings option there is checked.
Reboot just to make sure your changes take effect.
Once the computer reboots, you can see if it picked up its IP info automatically by opening a DOS box (MS-DOS Prompt) and typing the following command:
ipconfig /all
That should show DHCP to enabled, and should list your IP address, subnet mask, gateway IP, and DNS server addresses.
If the above doesn't work, post the info that the ipconfig command did report.
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