The following things may help.
1- Make sure you have the most recent version of your browser and Flash Player (You might also try to uninstall and reinstall them).
2- Clear cache and cookies of your computer. How to do this, is described HERE
3- Close all uploads, downloads or programs other than the ones used to play the game.
4- Check your internet connection (Try to unplug and plug back your internet router to reset the connection).
5- Try to connect to the game with a different browser (Chrome, Mozilla, Internet Explorer)
6- Try to connect to the game from another computer.