Answer
First examine your actual "C:\Program Files\nodejs" directory. Most of us already have a "nodejs" directory from a prior install, before we decided (or were told) to install nvm.
In the end, this "C:\Program Files\nodejs" directory will actually be a shortcut to where nvm manages the versions it installs (see C:\Users\xxx\AppData\Roaming\nvm). It seems that nvm is simply switching the shortcut, when we call "nvm use ...".
Ok, so here is what I did to fix the situation where "nvm use ..." was not taking effect.
- Delete/remove/uninstall the version of node in your "C:\Program Files\nodejs" directory. To the point where there is no more "nodejs" directory at all.
- Delete the existence of nvm (C:\Users\xxx\AppData\Roaming\nvm), basically, manually delete the nvm dir.
- Download your desired version of nvm (https://github.com/coreybutler/nvm-windows/releases)
- Open a CMD prompt (run as administrator), and install the downloaded version of nvm, nvm-setup.exe, from within this CMD command prompt.
- From within the admin level command prompt, run "nvm install 7.2.1", or whatever node version you want to install. Probably you will be installing multiple versions, so repeat as needed.
- Now do the usual "nvm use ...", "nvm list", etc...
I dont know if this is the best way, but it worked for me...