@hiruna-dilmith : most probably you have have a fresh clean installation of windows 10 pro version on your computer because most of the windows 10 keys sold in the internet are subjected to apply on fresh copy of windows 10 pro installation otherwise the keys won't be used. By the way why do you try to downgrade your windows 10 edition ? Windows 10 Enterprise edition is the highest grade edition in windows operating systems lineup with more features than the pro version. So, this is the most appropriate solution for now. If you need more clarification please give more details about this issue. Good luck !