How do I get a Linksys wireless router to work with my DSL internet?

I am looking for very detailed answers on how to set this up. We had everything working for a year. My roommate moved out (he set it up) and the DSL modem thing went out. SBC then sent us a new modem and the internet works when it is plugged in. The problem now is that wireless doesn't but it says that it is connected.

Any help? I don't know any passwords.