Package Manage Console not working

I am trying to install Npgsql and Npgsql.EntityFramework and getting this error:

Install-Package : The remote name could not be resolved: 'www.nuget.org'
At line:1 char:16
+ Install-Package <<<<  Npgsql
+ CategoryInfo          : NotSpecified: (:) [Install-Package], WebException
+ FullyQualifiedErrorId : NuGetCmdletUnhandledException,NuGet.PowerShell.Commands.InstallPackageCommand

What am I doing wrong? Please help