NODE_PATH changes on system restart

I have an issue with node_modules for node script. In my command line i have set the node path

set NODE_PATH=c:\..\node_modules

This works when i do

require('socket.io');

But when i restart my system, require('socket.io'); will not work, it says socket.io module is not found. When i again set my NODE_PATH via command line. It will work fine. So how to set my NODE_PATH, so that it wont changes when i restart my system.

Im using Windows

Thank you......