I have gone through similar topics and I think my case is not a duplicate.
Some 3 years ago, I had purchased a key for Windows 7 Professional from MSDN subscription. It worked fine and I've been getting Windows updates as necessary.
Now my system has become so slow that I'm thinking of re-installing Windows. I have the key with which I had activated Windows at that time. But I've been having a hard time trying to get an ISO.
I came across Microsoft Software Recovery but as expected, my product key was found to be invalid there.
Does that mean I can never re-install my Windows and continue with my same product key ever? Is there is no provision for OEM/MSDN licenses?