I'm curious, OP, yes, I realize this is a very old thread, and I am almost sure this was posted the same year that I had a similar problem. Did you have your slot drive replaced, and on an unrelated note, but since it happened to me, it may have happened to you.... Was your keyboard replaced.
On my old MBP that I don't own anymore. I ended up replacing the keyboard, the slot drive, and I think the top case. (I never figured out why the top case was replaced.)
I hope you have better luck with this problem than I had with my old MBP.