Unable to load the service index for source https://api.nuget.org/v3/index.json.

I installed dotnet-dev-win-x86.1.0.0-preview2-003156.exe on Windows 7 which I got fromhttps://www.microsoft.com/net/download/core#/current selecting Current/.NET Core 1.1 SDK - Installer/Windows/x86.exe. I followed the instructions in Getting started with ASP.NET Core:

mkdir aspnetcoreappcd aspnetcoreapp
dotnet new -t web

This produced the error: 

'dotnet' is not recognized as an internal or external command, operable program or batch file.

Then I executed:

"C:\Program Files\dotnet\dotnet.exe" new -t web

which seemed to work ok:

Created new C# project in D:\temp\aspnetcoreapp.

Then I exeduted:

"C:\Program Files\dotnet\dotnet.exe" restore

and I got the following error:

log : Restoring packages for D:\temp\aspnetcoreapp\project.json...
error: Unable to load the service index for source https://api.nuget.org/v3/index.json.
error: Response status code does not indicate success: 407 (authenticationrequired).

Can somebody help resolve this problem?