I was replacing my RAM y'day for my 13inch macpro, opening the back cover was very easy, but when I tried putting it back, two of the small screws won't tighten fully. A small part of the screw (25%) wont screw in completely. I can sense the the screw projection when I feel it with fingers. I tried the same angle as shown in the manual to unscrew and screw. And I took spl care to use the same screws for the same holes. I tried to fix it for 1hr, but the two small screws never fits. Any suggestions is greatly appreciated.