It looks like my project window (running windowed, not fullscreen) has hopped to some virtual space or other, because spacebar still initiates playback. I know there’s a way of moving the window, using the top-left-corner menu, but a) I can’t see it and b) I don’t know what its called, so can’t look it up.
Other projects open as normal.
You are on Windows, right?
In that case, when the project is open, hover with the mouse on the Dorico icon on the Taskbar until a little preview window appears. On that preview window do a right click and choose Move. You can then move the project window with the arrow keys (up, down, right, left) back into the visible area.
Ah, there it is! A bit battered but intact…