The number one tech support question we get is the issue of EndNote not showing up in the toolbar ribbon of Word. Often, the root cause of this is that MS Word was open when you attempted the first install of the plugin in.
Step 1: As a first step to troubleshoot, make sure MS Word is closed. Then try to re-install the .exe file. When prompted with a screen to Modify, Repair, or Remove the application, select Modify.
Step 2: Check to see if the Plugins are clear or have a Red X. If there is a Red X next to the plugin, open the drop down menu and select "Entire feature will be installed on a local hard drive."
Step 3: Follow the remaining instructions to complete the installation. Then open Word to see if the EndNote menu option is available.