Did you receive any error messages when you try to open Photoshop Lightroom? How are you trying to open the program?
I am having the same issue. I go to open it and I get, "com.apple.installer.pagecontroller error -1." I have NO idea what to do!!
This error usually occurs if you are not running Mac OS 10.6.8 and newer. You can find the required system requirements for Lightroom 4 at http://www.adobe.com/products/photoshop-lightroom/tech-specs.html.