You need to tell more about the setup and symptoms.
Have you located and re-read the literature which came with the router -- section about accessing the router's setup screens ?
Did you change ANYTHING between the last time it worked and when it failed.
Try checking TCP/IP Properties.
Start, Connect To, Connection, Properties, Scroll Down TCP/IP and highlight, click Properties and check that Obtain DNS and IP address automatically are enabled.
Have you tried restarting the modem and router together.
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