Upgraded to SQL Developer 4.0 and we are unable to create new connections in the Connections pane on the left hand side.
Clciking the green plus button and right clicking Connections and 'New Connection' doesn't bring up the New Database Connection dialog box.
Sounds like an 'install' problem.
Can you extract the zip to a new directory and try again? You did extract v4 to a fresh directory, yes?