(OUTDATED)Minecraft launcher not working (1.7.4)

Описание

(Oh dear what a video, im afraid I was not able to fix anything with this "solution")I have found out how to fix this but you need to play earlier versions of minecraft, but you still get to play minecraft!! http://www.youtube.com/watch?v=SmBfFAPWoks
click that link to see how.

(old description below)
I NEED HELP!!!!! I DONT KNOW HOW TO FIX THIS!!!! I open minecraft and the launcher appears, I press play, the launcher closes then opens minecraft, it shows the mojang log for a couple seconds, then minecraft closes and the launcher reappears. I don't know what to do to make it work again.