MacBook Air shows white screen at login

When I turn my MacBook on, it shows my login and lets me choose a user. I type in my password, and it freezes for a while, tells me I "shut down my computer because of a problem," then the screen goes white. I've tried flashing the PRAM, restarting it over and over again, nothing seems to work. It's still responsive, I can move my cursor around and if I press the power button, the little menu shows up.