You can only use an activation code once. The license is still on the dongle. You do not need to activate it again. Just install Cubase, plug-in the dongle and get to work. If you are talking about the message that prompts you to REGISTER Cubase, just click, “Already Registered”.
BTW, I am assuming you are talking about the full version of Cubase (with a hardware dongle). If you are talking about Elements, there is an article in the knowledge base about reactivating your software E-License on a new laptop or hard drive.
HTH
J.L.