Windows 10 Problem in upgrading Windows 10

[Nishant]

I was not able to upgrade to Windows 10. Every time, the process failed after 60-70℅. So at last I tried to install windows 10 through media tool. I succeeded but now I am not able to activate Windows 10 using my key of Windows 8.
Can I go back to Windows 8 and activate it using my key?

 

[kemical]

Hi,
If you have the windows 8 disk and activation key then you should be fine.