Did your mom use that activation code for installing Cubase? In that case you can not use it anymore, these codes are one time codes.
Also Cubase LE 5 is a pretty ancient release, the current version is Cubase LE 15.
However, you can try to add a request for an update of your release by adding it to this thread (at the end) asking @Ed_Doll or @Matthias_Quellmann to put it into your account.