Turned on my MB PRO to see the grey screen with "Flashing Folder w/ Question Mark." After booting up online, I could not mount the hard drive in order to designate it as the start up disk. These models are known to have a harddrive cable issue, and my MB Pro travels to and from work for 5+ years, 5-6 days a week.
Smooth. 25 minutes later . . . I'm backing up all of my HD files. Good luck.
The best advice I can offer is to purchase the #00 screwdriver to open the unibody. Also, beware that the 7 small screws are not all the same.