When Creating a new Angular 5 project:
node version: 8.9.2
npm version: 5.5.1
My Command is
npm install -g @angular/cli
This solved it for me:
Open Windows Powershell as admin
npm cache clean --force npm install -g @angular/cli
https://devblogs.microsoft.com/premier-developer/getting-started-with-node-js-angular-and-visual-studio-code/