run in cmd

 npm install -g @angular/cli

and then

( open in Windows 10) Control Panel\All Control Panel Items\System or accordance with the figure

step 1:

step 2 :

step3:

step4:

step5: add missing ng path

C:\\Users\\{your username}\\AppData\\Roaming\\npm
C:\\Users\\{yourusername}\\AppData\\Roaming\\npm\\node_modules\\@angular\\cli\\bin

Here is new environment variable that you need add: C:\\Users\\AD\\AppData\\Roaming\\npm\\node_modules\\@angular\\cli\\bin

Finally, restart all opened command prompts and try again.