1.6.11 Not Starting.....

I am unable to start 1.6.11 on either my Mac or PC, I get the splash screen for about 2 seconds then nothing…

Please run arduino_debug and post the output. There are probably quite a few different reasons this could happen but my first instinct is it's the issue described at http://forum.arduino.cc/index.php?topic=419071.msg2885938#msg2885938, an incorrectly formatted 3rd party hardware package. These worked with previous versions of the IDE but if you had installed one before updating to 1.6.11 then 1.6.11 doesn't start. Could this be your issue?