|You had an account with one isp; you changed your isp; you therefore will have a different account with the second isp to that of the first?|
With the first isp you will have one username and password etc. for that account; and it will be highly unlikely that your "new" (second) isp will have given you exactly the same username/password.
Your cable modem will require that "new" information entered into its setup to enable you logon to your "new/second" isp service. Otherwise as the user name/password (account details) for the first isp will be still be in the cable modem setup, you will not be able to logon (the cable modem) to your new/second" isp?
If per chance your second ips provided the cable modem, and it came effectively preconfigured (your account details - user name/logon and password already entered into its setup) then you won't need that info (although it's rather useful/wise to know what it is regardless).
Perhaps useful to clarify your actual situation.problem; incase I've misunderstood/misinterpreted your situation...?
Using an ethernet/cat-5 connection between the router and the modem can you get on-line, if you connect your computer to the router via an ethernet/cat-5 cable?
And if so then are you asking how to setup the wifi aspect of the router?