Have you ever opened Photo Mechanic on a second monitor or changed the resolution of your monitor? It's been a while since I've experienced this, but I believe that there is or was an issue (it may have been fixed in Photo Mechanic 6, but I'm not sure) where a window's position can be saved in a location that is off-screen.
In my testing, the window position was saved in the registry key (I deleted the Photo Mechanic registry key after moving the Find window and the window went back to its default location). If you know where to find these and how to reset them, I would recommend doing that. If you're not sure, please give us a call at 503-547-2888, as it's simpler to walk through it over the phone.