I’m sorry for the inconvenience!
How many pages are there in your project? When you first click in the edit control after choosing ‘Page Range’, I would expect the preview on the left to go blank because there’s no valid range yet, but you should then be able to type e.g. “1” and almost right away the first page of the layout should appear in the preview area.
Would you be able to capture a log during the hang so we can take a look and see what’s going on? You will need the Process Monitor application from Microsoft/Sysinternals, which is a free download here. When you run Process Monitor, stop it from capturing everything by clicking the Capture button (which looks like a magnifying glass) and clear everything it’s captured to date (the button has an eraser on it). Create a filter for “Dorico.exe”, start capturing, then try and enter a page range. Once Dorico has hung, return to Process Monitor, stop capturing, and save the resulting log. Please then zip it up and attach it here or email it to me at d dot spreadbury at steinberg dot de (please include a link to this thread if you do that, so I can remember what I’m supposed to do with it), and we’ll take a look.