Have you tried to completely uninstall NWjs, even looked if the folder is deleted and then reinstalled it?
I had in my export some wired folder named alt and neu (old and new) and there was a nwjs exe in it what opened an empty screen with an address-bar.
But after the reinstall it all worked without a problem.
I suggest in hindsight, that the old nwjs 0.12 caused the problem not my old node.js.
Have you installed the new beta 4 over the old nwjs installation?