Sounds like it is off screen.

Did you have a second monitor plugged in before and now you don't?

Are you on Windows? If so you can "grab" the window as if to move it.

Tap the taskbar button for Poser so it has focus. Then type Alt-Space M Left-arrow

(Hold alt, hit the space bar, release alt, hit the m key, hit the left-arrow key)

You are now moving the window - move the mouse around and see if you can find it.

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Renderosity forum reply notifications are wonky. If I read a follow-up in a thread, but I don't myself reply, then notifications no longer happen AT ALL on that thread. So if I seem to be ignoring a question, that's why. (Updated September 23, 2019)