Check 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.
Also check that your wireless is working properly -- see router manual for how to address router's setup screens.
If you can get into the router's setup wirelessly, it suggests the issue is beyond the router. If you can't, connect the computer to router with an ethernet cable and, if that works, your wireless settings probably need adjusting.