I've run into this issue a few times so I figured others have too.
Once in a while Cura's main window doesn't show up. Here's what I think fixes the problem. I say I think because I don't entirely know because I've tried so many things.
1. Reboot the computer
2. Rename the file:
/Users/cbensen/Library/Application Support/Cura
to something else.
3. Download a newer version of Cura here:
https://www.lulzbot.com/cura
If there is no later version, then try the latest developer version here:
http://devel.lulzbot.com/software/Cura/mac/
4. Copy to the desktop because you don't want to loose the older version.
5. Run.
Hopefully it works.
