Having read other postings in this forum raising the same or a very similar query, I understand that you need to delete the demo version first otherwise it will default to the demo mode. Trawl back through previous postings that seem to have the same subject heading as yours for an answer.. The official answer is provided by jroberts (Laminar Research - X-plane).
Do you insert disc 1 into your disc drive? I understand that if you don't the program will always default to the demo mode.