i just replaced my hard drive today. i booted it up and went to disk utilities to format it and all of that. When i finished i went to restore system from back up and plugged in my external hard drive and the computer said there was no history of back up. This was strange because before i formated the hard drive and tried to restore the information, it recognized that there was back up information. I decided i would re-install the os and try again. Any help is appreciated.