windows 7 pro 64bit reactivation

[ADITYA_19]

I have purchased windows 7 pro 64 bit ,.and successfully installed and activated using the product key and then I upgraded my pc to windows 10 pro 64 bit, after 2 months due to some reasons I have reset my pc and reinstalled windows 7 pro, but not from the installation disk, but I have the product key and somehow I managed to install windows from ISO file, and if I use the product key now for activation it shows error invalid product key. Can't I use the same product key for installing same version of windows on same pc? even i can't login to Microsoft account from my pc as I am on windows 7 pro and I even can't upgrade too, contacted Microsoft chat support but not seem to help, but they told while I am chatting "your product key is working and can be used again" but I tried all the ways I know,.. nothing helped me yet please someone help me to activate windows.

 

[ex_bubblehead]

30 days after you upgraded to Windows 10 your Windows 7 license was permanently converted into a Windows 10 license. You cannot reuse that key with Windows 7.

 

[ADITYA_19]

but i can't even use that key with windows 10 pro also ...!!! it showing me same error,.. what can i do? but Microsoft chat support member told me that the key is working one,..i don't know where the problem exactly was?