Alright first I thought it was a drive failure but now I know it wasn't. I took the hard drive out of my daughter Macbook Pro mid 2009 and installed the hard drive out of my Macbook Pro mid 2009 both 13 inch. Her computer won't boot to my drive when I know it's working fine. I get the apple and the spinning wheel and that's as far as it goes. After time I will get a circle with a line through it. Any ideas what could be causing this?