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
Short answer:
Just install the latest version of nodejs and then restart your system.
more description:
It's related to Environment variables in your system at least as far as I know, you can make changes in path variable in your system as others talked about it in the current thread but the easiest way to solve this is installing nodejs!