Don't know which modem you are using, so I will talk about my Westell 6100. It has NAT capability so some of the issues discussed earlier can pertain to the modem when router is not in use. A google search for "Westell 6100 manual" was productive. There may be some info here that will help you with your problem. You can also search for the manual for your modem.

I assume that you beyond this step. Did you create a new network connection on that laptop?