How long have you waited? If something is querying a network drive that doesn't exist on the network, Windows can take up to 30 seconds for that to timeout, which can sometimes block the window. (In Opus 13, you'll see a message informing you about it in most cases, and can cancel it. Opus 12 doesn't have that though.)
If the window is frozen for longer than a minute, please make some snapshots and send them to us, and we may be able to see what's wrong from those.