No internet service

Hello, I recently had a new optonline modem installed for phone and internet.prior to that I had a separate phone, wireless and internet router. Since the set up of the new optonline router, one of 3 laptops is now unable to get internet service. I was working with linksys ( wireless router ) to set up a NEW wireless router on the laptop that is now not working . I am running on windows xp professional . dell inspiron 6000 notebook. processor 725 .
I have a linksys wireless router with security. the diagnostics on the laptop report the dns unreachable. Please advise.