sql developer hangs on startup - what can I do?

Deleting files from c:\Users\MY_USER\AppData\Roaming\SQL Developer\SQL History and c:\Users\MY_USER\AppData\Roaming\SQL Developer\System... Really helped me to resolve the connection issues

Remove folders c:\Users\USERNAME\AppData\Roaming\SQL Developer\system4.1.3.20.78\system_cache*. SQLDeveloper will recreate it after launching.

Basing on this thread https://community.oracle.com/thread/2564842 I've created own solution.

1. Extract installation of current version SQL Developer (4.1.0.17.29)
2. At "c:\Users\MY_USER\AppData\Roaming\SQL Developer\" I've changed directory name system4.1.0.17.29 to system4.1.0.17.28.
3. After running newly extracted SQL Developer (4.1.0.17.29) I was prompted to let copy configuration from version 4.1.0.17.28 to 4.1.0.17.29 ;)
4. Everything works great now. I suppose that running the same (broken) installation after decreasing version could also help.