Can't open Minecraft after leaving Beta without the window closing on me. Please help.

I did join the Beta, but then I realized I wouldn't be able to play with my friends so I left. When I tried clicking to once again open Minecraft, I realized it would open the window, I would see "MOJANG" pop up but, the window would immediately close on me. This keeps happening and I don't know how to stop it. I wish to keep my worlds so I don't wanna risk deleting Minecraft and then downloading again. Please, help if you can.