I usually get this when the VSTAudioEngine is still running (most likely after a Dorico crash) so Dorico stalls out when trying to initialize that process. In Task Manager, close Dorico and the VSTAudioEngine process, then try starting Dorico again.
If Todd’s advice doesn’t help, restart your computer altogether, then try running Dorico again. If you get as far as the Hub, choose Help > Create Diagnostic Report and attach the resulting zip file here.
Obviously I don’t know if it’s feasible or not (just thinking out loud here), but it would sure be neat if, immediately upon being launched, Dorico could check the status of the VSTAudioEngine process and if it’s running then kill it, and then proceed with the normal start-up process. (I’m sure Daniel and team have already thought about this, and since Dorico doesn’t do this it most likely means it can’t be done, but it’s a fun thought anyway…)