Error: 'ng' is not recognized as an internal or external command

Reason for the issue is:

1. Either Env variable is not setup properly
2. or  angular cli is not installed globally so 

Solutions:

1. open command prompt, press (ctr + r) and type cmd
2.  run this command "npm install -g @angular/cli"
3. and all set for you to just verify go to cmd and type "ng" you will get all the details as the problem has be solved.