Help!!!! My game is being uber dumb. (MAC)

So I have league downloaded on my mac and I couldn't open it anymore. The Icon would pop up on the dash for half a second after clicking the icon, but it closes right after. I tried re-downloading the game but it usually stops somewhere around 76-89 percent at (0KBps). I love the game and really want to play. I've been trying to open up the "old" fully updated icon on my desktop and re-downloading it. Can anyone please help?