I just want to re-submit a known bug that hasn't been fixed so far. Changing from Oracle LaF (Look and Feel) to Windows LaF will prevent SQL Developer from showing the GUI even though sqldeveloper.exe is running.
Environment:
Windows 7 Ultimate SP1 64-bit.
SQL Developer 1.5.5 build MAIN-5969 (latest version)
Java 8 update 5
Followed this discussion to solve the issue:
How to solve it on Windows 7:
Terminate sqldeveloper.exe on Task Manager.
Go to %appdata%\Roaming\SQL Developer\system1.5.5.59.69\o.sqldeveloper.11.1.1.59.69
Open product-preferences.xml
Find:
<value n="lafClass" v="com.sun.java.swing.plaf.windows.WindowsLookAndFeel"/>
<value n="lafThemeClass" v=""/>
Change for:
<value n="lafClass" v="oracle.bali.ewt.olaf2.OracleLookAndFeel"/>
<value n="lafThemeClass" v="skin:fusionblue"/>
Save changes.
Done.
Hope this help anyone