Try selecting it on the Windows taskbar, then use Win + Left or Win + Right a few times until it appears.
(It shouldn't normally need that, as it should ensure it opens on-screen and move itself if the last used position isn't visible anymore, but maybe that's going wrong or there's a screen that's turned off which Windows still considers there.)
If you're using these tools, or similar ones, then they could also be involved, although I haven't heard of them affecting Preferences so far: