MacBook Pro Lion crashes after a progress bar boot
It could be a few different things that are causing this issue.

I would highly recommend taking your computer in to the Genius Bar at your local Apple Store and having them take a look at it. 

http://www.apple.com/retail/geniusbar/

Its free for the appointment and the diagnostic even if you are out of warranty and will probably be the fastest and easiest way to get to the bottom of what is happening with your machine.  

I know its not an instant fix but it will make things a lot easier to have them look at it.