Fixed! 2013 Macbook Pro 13' Unbody 2012
One day my computer was acting up by freezing during a function which ultimately restarted my computer. During the boot I got a grey screen with a folder "?". I did a OS X recovery, pulled up the disk utility to find that my HDD was not physically there.
The repair went well, the website provides a easy step by step process to remove the exact parts to replace what you need to repair. It was helpful that the website also provides what type of tools to use.
I thought that either my HDD unmounted or the drive was corrupted. I reviewed numerous websites about similar postings about the same issue. I found that unbody 2012 edition macbook pro 13' had hard drive cable issues. Normally people will just replace the hard drive right away but I found that you should replace the hard drive cable first before replacing the drive. If the drive was corrupt you computer will not be able to boot up at all.