About a year and a half ago I dropped my MBP ever so slightly on the floor. It was in my messenger bag and the strap slid from my shoulder. I was able to catch it, but the corner of the bag hit the ground. When I opened my MBP - which was in sleep mode -everything froze. After a reboot the question mark folder popped up. My hard drive had died. Or so I thought.
After replacing the hard drive, nothing happened. The problem was there to stay. So I took the hard drive back to the store and bought an external one instead. I installed OSX on that one, and lived about a year and a half with OSX on that drive. I wa too low on money to have an expert look at it.
Then a friend of mine got the same problem, and it appeared that his SATA cable was broken. So then I was almost positive it was my SATA cable, not the hard drive that had to be replaced. I had no money to have someone do it, so I stumbled upon ifixit and the rest is history.
The repair was fairly easy, although I kind of had experience doing it when I replaced my HDD. However, I found that two of the three battery clips had broken off, so I might need to replace that one day :')
Be patient and repair your laptop under well lit circumstances. You're handling a thousand+ dollar machine, so take care of it. Don't rush anything. Print the guide up front or read it on a phone or tablet. Stay positive. It's easier than it looks.