Since updating to Mac OS X 10.11 (Yosemite), Mathematica 10.0 will not start. I just get the spinning beachball, with no error messages, but it does not crash. I've tried suggested fixes (Deleting Library/Mathematica/Paclet, and re-installing Java SE 6) but nothing has helped. There is no error code and the console log is not helpful (to me).
I would try updating Mathematica to 10.3, but the dmg file from Wolfram won't open! It is not recognized.
Any suggestions? Any ideas of how to see where things are failing?