Macbook won't start?

I am trying to fix my laptop myself before I have to take it to the genius bar.

I press the start button and the password page displays straight away, but with a white background not the usual transparent background, I enter the password and am then taken to the load bar page, when the bar gets to about 1/5th loaded the entire thing shuts down.

I have tried recovery mode and verifying the disk in disk utility, but there are no errors.

I have no idea what is wrong

help?