cable modem instalation

Ihave a cable modem connected to an 8 port ethernet switch. 4 computers are connected to this switch and are working perfectly. I’ll try to connect a new cable modem to the same cable line just to only one computer and it is always reject the internet connection telling me and error. My question is can I use a different cable modem to the same line or I have to call the cable company for the ew modem ? Are the IP address change or the DNS are different? Why the cable modem that the company sold me works and the one I bought no?