如何修复Windows 10中的composer.phar安装错误？

Question

I've been googling this for half an hour and nothing's working. I've got PHP added to my windows path variable, and everytime I run this:

php composer.phar install --no-dev --optimize-autoloader

I get this

Fatal error: Uncaught exception 'PharException' with message 'unable to open phar for reading "composer.phar"' in composer.phar:23
Stack trace:
#0 composer.phar(23): Phar::mapPhar('composer.phar')
#1 {main}
  thrown in composer.phar on line 23

I'm CD'd into the folder it's in, I've tried specifying that folder in the command, nothing's working, neither does

php -r "readfile('https://getcomposer.org/installer');" | php

edit: Ok I signed out and back in after trying the windows exe installer, seems it's installed now but only globally, I still don't have the vendor/bin directory I need in my specific project, still fails when I try and run php composer.phar install