Thank you. I have reinstalled Windows 10 on my working computer and the serial number did not need to be entered and it will be activated automatically.

If I have any questions on Windows 10, I...

Thank you for explaining. I understand now. My final question is "Can I use the previous Windows (7, 8, 8..1) serial key with Windows 10?" It seems I can use that.
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Thank you so much. I will ask my supervisor to acquire the serial key of Windows 10 installation or should I find the serial key on other computer?

I am using Windows 10 for working. On that computer, I cannot click "start menu" and the app can't be opened. When I open the pictures in the app and the picture app can open the pictures. However,...