Hi @robert_chadwick2 , welcome to the forum and don’t worry we will get you there.
So you have Dorico 4 installed and sound with that one, right?
When installing Dorico5, did you also install the new HALion Sonic Selection content? If not, then please do that. Then also follow the advice as given by Daniel in this thread. That should let you going. Should you still have trouble, come back here, I have more advice to give.