I've re-installed. Do I need a new key?

Every installation will require its own activation key content its own unique registration code.

If you've re-installed then any previous codes/keys will no longer be valid.

You'll need to register again in the usual fashion.

It is important to know that these are not a one-size-fits-all key.
Be sure that the registration number you submitted belongs to the computer and the specific installation you are trying to use the key for.