Solution: SQL Developer does not show its Startscreen after starting successfully

Problem: 

After starting SQL Developer 18.4 on a Windows 10, the SQL Developer tile is shown in the taskbar, but the Startscreen is not shown on the desktop.

"Quick and Dirty" Solution

• Stop SQL Developer. 
• Open Windows Explorer and type "%APPDATA%\SQL Developer" in the Directory/URL bar. You'll see a directory named according the SQL Developer release (for example, something like "system18.4.0.376.1900"). 
• Rename this directory.
• Start SQL Developer - the directory is re-created, everything should work fine again. If SQL Developer comes up correctly, delete the renamed directory from "%APPDATA%\SQL Developer"
• get back to work ... ;-)