I have a Mid 2009 13" MacBook Pro that won't boot up. Everytime it gets stuck on the Apple load screen and a little progress bar goes along the bottom. I've let it go all of the way across, but then the dail below the apple just spins and spins and spins... UGH. What's wrong here? My computer froze on a screen, and it was freezing intermittently just recently, so I forced shut - down it and now it won't turn on.