Crash on label

Whenever I load minecraft up and start, it would crash after loading the "Mojang" sign. It does that on 1.7.5 too. So I can't play with any of my friends!

Here is what happens:

1. I click the minecraft app on my computer
2. I hit "Run".
3. I press play. (While logged in)
4. it does the mojang sign.
5.It goes back to the "Play" Button!

This is really annoying, but I love your games! I have Minecraft on pc, xbox and Ipod and I want to play Minecraft on pc again!