Is your PC connected directly to the cable modem? Check if your PC has been allocated an IP address:
Go to the Local Area Connection Status. General shows you the number of incoming and outgoing packets. Click Support. You should see the external IP address, allocated by your ISP (if your PC is connected directly to the modem) and the default gateway, in your ISP's network.
Click the button Details. Is there an entry for DSN Servers?
If you have a router between your PC and the cable modem, it is a slightly different matter. Then your PC will need an internal IP address in the range e.g. 192.168.1.0 and the gateway will be the internal IP address of your modem. Additionally, the DNS server address could be that of your modem, assuming that the DNS proxy server in the cable modem has been activated.
I do not know the Roadrunner environment. Did your modem come with a setup CD?
Usually it is possible to use the browser to access the admin interface in the cable modem. One of the options will then tell you what the connection status of the modem is.
If the login name and the password are not right, you can still see the number of packets increase.
Last, but not least, RTFM (read the manual) and speak to the helpline of your ISP.