Mathematica won't start on my Yosemite Macbook Pro

Questions
1

It’s worked before. One day I click on the the icon, it bounces for a long time and then it just stops and I have to force quit it. What do I do?

2

Please see this post

http://mathematica.stackexchange.com/questions/92931/mathematica-10-0-x-freezes-in-initializing-kernels