If it does not activate correctly then you need to enter a valid code, (unless you are on a network that has a corporate KMS Server) If that is the case speak to your IT.
If you dont know what version you installed then run the following command and it will tell you
slmgr -ipk 12345-ABCDE-12345-ABCDE-12345
Once it accept the correct code then simply rerun
Cut and paste the following into Notepad
Open in new window
Save to your desktop as wm.bat
then right-click on it and choose Run as administrator
You should get a "success" message and the watermark disappear
If so then restart Windows to check it has gone for good!