By skyforbes 
1. Ensure you are running the latest node and npm version
2. Run where ng command and copy the directory (e.g C:\Users\user\AppData\Roaming\npm\ )
3. Add the directory to SYTEM PATH by right clicking on This PC, go to properties, go to advanced system settings, then click Environment Variables
4. Restart the computer to save the changes
5. If that does not work try uninstalling and installing angular cli again