Freezes after restart

I updated my 2009 MacBook Pro to Mavericks and on the final restart it freezes. I've crashed it twice now and restarted again, but it makes no difference. The same screen (light gray with a dark grey apple in the center) is frozen for hours. I'm really at a loss for what to do. I'm a freelance graphic designer and I need this computer to work. Please someone help! I was on the most recent update of Mountain Lion before this point.