I would like to reset my old laptop with Win7 Home Premium because getting started a program DirectX could not be initialized. The question is, can I reuse my used key on the laptop when I put in back?
Can you.
Theoretically yes, practically it can cause problems.
In this case, however, there's a free hotline that unbureaucratically unblock the thing.
You know that the key is also accepted for Win 10? So you could instantly install Win 10 instead of Win 7.
That's fine. Unless the key comes from a "dark" source. Some such keys only go once. Then no hotline will help.