The download assistant will not open so that I can activate Dorico 5

Welcome to the forum, Mark. Are you trying to enter your Download Access Code received from the Steinberg online shop in your receipt email? If so, you can enter that here. If you need to download Dorico 5 and can’t get SDA to run, you can download everything you need from here:

Thanks much! that worked thank you for your speedy response to my inquiry!