ng : File C:\Users\YAZHINI\AppData\Roaming\npm\ng.ps1 cannot be loaded because running scripts is disabled on this system. For more information, see about_Execution_Policies at https:/go.microsoft.com/fwlink/?LinkID=135170. At line:1 char:1 code example

run the below command 

Set-ExecutionPolicy -ExecutionPolicy RemoteSigned -Scope CurrentUser