I have just changed computer (Windows 10) and have installed and activated Kontakt 4 with no problems. After installing the Kontakt 4 programme from disc, I opened Native Instruments (latest version). I enabled "Legacy Products" under Options. Kontakt 4 did not appear in any list but I clicked "Add a serial number" and put in the K4 serial number from the back of the package. K4 activated at once.