the minecraft game does not want to start

Put the summary of the bug you're having here
i am having trouble starting the minecraft 1.6.2 game
What I expected to happen was...: the version i was trying to start was not the version i have in my computer
Describe what you thought should happen here

*What actually happened was...:*something pops out every time i am trying to play demo
Describe what happened here

Steps to Reproduce:
1. Put a step by step guide on how to trigger the bug here
2. ...
3. ...