Help with DSL connection

I have recently purchased high speed internet through Embarq. I cannot get connected to the internet with my iMac. All I get is a message that "The Specified Server Cannot be found". When I run diagnostics, it tells me that I am not connected to the internet. I spoke with a couple of different tech folks at Embarq, and they say that nothing is wrong with their equipment, which I believe for when I hook it up to a Dell, it works fine. They ran me through several "experiments" but nothing works. I'm sure someone out there can help!!!