When I press play, nothing happens!

I will try to make this as detailed as possible..

After I open the launcher, I press ''play''. It the prepares the game. But, after that, nothing happens! Literally nothing! But, if I press play again, this message comes up:

WARNING! Game already running.

Then, I can either press ''Cancel'' or ''Start anyway''. And, when I press ''Start anyway'' it prepares the game again. But still, nothing happens! I do that over and over again, but it just doesn't work. 

This is as detailed I could get it.