Why isn't my wireless connection working?

I have an old titanium G4 powerbook with a airport card. I am staying in a new place for a month and while my computer picks up a full wireless signal and says it is connected to the network, it won’t let me on the internet. Everytime I try to get online the error message comes up saying it can’t find the host. Its driving me crazy because it had been working fine and suddenly just isn’t anymore. Other people with mac and pcs are having no trouble connecting.