Restarting the cable modem is often the best first step in troubleshooting as it can resolve a range of issues, including ones related to connection establishment with the Internet Service Provider (ISP). Replacing the modem or router would be more costly and time-consuming without first attempting simpler troubleshooting steps. Checking the network card would not be related to a modem's inability to connect to the ISP. Cable testing is useful for ensuring physical connectivity but the scenario has verified physical connection.