The Page Creator V6 application isn't available anymore which means it's impossible to buy a new version. There is no website configured or a way to buy it. In this case, the only thing you can do is to try reinstalling it, but this time do it with Administrator rights and after installation, right click the executable file and choose Properties > Compatibility. Choose an older version from the list (eg. Windows XP) and then run it again and register.
Of course, it is also possible, the key has expired.