My computer was unresponsive, rainbow wheel and not working at all... So i tried changing the RAM which did nothing. I changed the Hard Drive and it didn't work either. Finally i decided that the cable between the hard drive and the logic board must be defective... so i got a friend that has the same macbook pro as me an changed his cable for mine and the computer worked flawlessly.
15 minutes tops to repair... very easy. Decided not to use the adhesive tape because if i messed up the position i could have had a very hard time trying to repair it.
Follow instructions to the letter. Small screwdriver with magnetized point.