I wonder whether it could be a licensing issue? Do you have the most up-to-date version of Steinberg Activation Manager installed? Is your Dorico Pro 4 license correctly activated?
If you can’t get Dorico to start all the way up, you could try using the scripts in this thread:
to generate an ersatz diagnostics report that you can upload here, and we can then take a look and see if we can figure out what’s going on.