Multiple Networks Conflicting

I just purchased a new Dell Inspirion desktop. I plugged my DSL into it and
everthying worked fine the first time. However, after shutting down the PC
and every time since that I restart it, when it comes back up two networks
appear in Network and Sharing, one public and on unknow private network.
Because there are two, I can't connect to the internet. I first have to
either disable one, which disables both, and then re-enable the one I want or
I can diagnose and repair. Can anyone tell me why a second network keeps
appearing and how to stop it from appearing?

Thanks.