Something like this has happened to me re-arranging my monitor setup. I use 3 monitors, but at times I've plugged in one to another computer I'm debugging/fixing/building, and reduced my Windows setup to 2 monitors.

Some applications will launch their dialogs in a 'previous' location which they remember, and sometimes that has meant that it was shown so far to the right that it was on my 3rd monitor, which once it was removed, made the dialog out of view and not visible.

I can't say that's what's happening to you, but it's one reason it has happened to me.