I'm working with BikeCAD Pro on my laptop which is connected to an external screen half of the time. At some point I must have moved the "Display" window onto the secondary screen and today, with only the primary screen available, "Display" didn't appear.
I figured out that by changing
<entry key="LocY DISPLAY">1662</entry>
in dialogs1.xml to
<entry key="LocY DISPLAY">162</entry>
I could make it reappear again. Please make sure that you display windows within currently available screen borders, only. Even if the stored dimensions were once valid.