I finished my app and I have to bring it for company to show them what it is and how it works. I dont need any hosting service since there is(in company) their own network. So I thought I might just copy the whole app on my pendrive, just like that. Obviously I got plenty errors so I decided to compress it and then move. It worked, I have my app moved from Ubuntu to my pendrive and for tests, I moved it out to my Windows. There problems start to begin.. I did install nodejs, obviously unpack the folder, did write " npm install " twice( once at the server-side to download the node_modules from there and once at the client-side) and I still keep getting the error : 
About my app: Its a MERN stack with Redux, some bootstrap. There is obviously lots of node_modules like nodemon, concurrently, etc,etc..
Thanks for any try to help <3
Looks like you have't installed nodemon globally on the new OS.
Try:
npm install -g nodemon
And see if that works
Edit: You are now getting the error "react-scripts is not recognized as an internal or external command..." yada yada... You could install react-scripts, although it should be installed already.
npm install react-scripts
Check this question and try the suggested solutions: