If you can't open your files (.mdj), then please check the followings:
1. Network drive is not supported.
Network drive is not supported yet in StarUML. If your file is in a network drive, you cannot open it. Try to open it after copying it into your local drive.
2. Open your diagram by double clicking.
Many users are not aware that a model file (.mdj) can have multiple diagrams. When you open a .mdj file, you may not see any diagram immediately. In that case, you have to open the diagram by double clicking on the diagram node in Model Explorer (a treeview in the right top area). If you cannot find any diagram node, please expand the every tree nodes. Once a diagram opened, StarUML remember the diagram and try to open the diagram automatically when you load the .mdj file.
Thanks,
StarUML Team