Minecraft 1.8.3 on Mac OS X blocked after a few seconds

Hi,
I have bought Minecraft 1.8.3 on MAC OS X.
It has worked for a few days, and then each time I play, the game slows down and blocks after a few seconds.
I have found several advices on the web :

• increase the memory parameter in a config file : done
• upgrade java : done, I have the 14.9 version
• uninstall/re install minecraft : done
  What can I do then?
  Thanks you for your help.