Elikadam

So, I am pressing play. It acts like it is going to start up and load but after a few seconds it goes back to the launcher and says play again. I am unsure if it is my laptop or the launcher itself. I uninstalled and reinstalled the launcher, the mod packs and updated and restarted my laptop. I play on a mac OSX, it has 4 GB Ram and more than enough memory space. If I could get some help to understand why its doing this id be grateful cause i was playing just fine yesterday. Thank you guys in advance, i know your super busy so when you have time to help id be thankful.