First,

Be sure that you have gulp and gulp.cmd (use windows search )

Then,

Copy the path of gulp.cmd ( C:\Users\XXXX\AppData\Roaming\npm)

Add this path to the Path envirement variable.

*OR

Edit “PATH” environment variable and add %APPDATA%\npm
(Add %APPDATA%\npm to front of Path, not end of the Path.)

finally,

reopen cmd.