EndNote is asking me for a license number or product key -- do you have it?
Usually this means you need to reinstall Endnote. Uninstall the version you have, and use the Northeastern student portal or the employee portal at me.northeastern.edu. Go to Resources-->Software-->Software downloads and download the Northeastern-customized version of Endnote, following the instructions on the Snell Library EndNote information page.
Especially in the Windows environment, be sure to right-click/extract all on the zip file before installing.
DO NOT just click on the zip file. You MUST extract it first.
If you do not extract the zip file prior to installing, you will continue to be prompted for a license key and you will not be able to complete the installation.