Hello - not familiar with how Windows handles window management, but it could be that it is indeed offscreen somewhere and you'll need to move it. You can try using the Windows + Shift  + Left or Right arrow key combination to move the monitor and see if it shows up across one of the monitors - you can also try altering or deleting your configuration file in case MasterPlan remembers the window position in an invalid location. To do this, you can find it in: C:/Users/<Username>/AppData/Local/MasterPlan/settings08.json - you can try changing the "WindowPosition" > "X" and "Y" values to be in sensible locations, and ensure the "W" and "H" values are logical (i.e. not 1x1 or something like that). You can also try just renaming the config file to easily restore default values and see if the program shows up in a logical location again.