Cable modems remember the Mac (hardware) address of the last device to connect to them, and typically will not give any other device an IP address. If your modem has a reset button, that may get it to work. But otherwise when you connect a different device to a cable modem, disconnect power from the modem for a few minutes, power it up until it does its thing and is stable, then power up whatever is connected to the modem on your side.If you are regularly changing things or want to connect more than one device (or wireless devices) to the internet, a broadband router can make that much easier (wireless router if you do or might use WiFi).
Cable modems remember the Mac (hardware) address of the last device to connect to them, and typically will not give any other device an IP address. If your modem has a reset button, that may get it to work. But otherwise when you connect a different device to a cable modem, disconnect power from the modem for a few minutes, power it up until it does its thing and is stable, then power up whatever is connected to the modem on your side.If you are regularly changing things or want to connect more than one device (or wireless devices) to the internet, a broadband router can make that much easier (wireless router if you do or might use WiFi).