If you have downloaded EndNote X9 for Windows:

Extract the EndNote files from the downloaded zip folder (see image below and steps 1-3 in the EndNote X8 instructions) Run ENX9Inst.exe When prompted to enter the Product Key, copy and paste it (Ctrl V) from the Endnote_9_activation.txt file that was unzipped into the same folder (ENX9Inst_Win) as the executable file

If EndNote X8 asks for a Product Key after downloading and installing from the McGill Library website, do the following:

Download EndNote again: http://mcgill.libanswers.com/citation/faq/53817 Then, open it once the download is finished. Click the Extract to or Extract all files link to run the Extraction Wizard (extraction steps may differ based on your OS and what software you are using, e.g. WinRar or WinZip).This is very important! When the compressed folder has been extracted, go to the location where it has been saved (which should open automatically for you). Double-click on ENX8Inst.msi to run the software installation.

EndNote X8 should not ask for a Product Key following these instructions.