I tried running npm install -g angular-cli
I also tried adding it to the Enviorment Variables under PATH: (C:\\Users\\Administrator\\AppData\\Roaming\\npm\\node
If angular cli is installed and ng command is not working then please see below suggestion, it may work
In my case problem was with npm config file (.npmrc ) which is available at C:\Users{user}. That file does not contain line
registry https://registry.npmjs.org/=true. When i have added that line command started working. Use below command to edit config file. Edit file and save. Try to run command again. It should work now.
npm config edit