If your button to open mac is hard to use after you re-assembled the computer, check to see if the proper length screws were reinstalled. I had that problem and I switched the 2 screws. One was a tad longer. The longer one when screwed in, interferred with the button function.
The 2 screws I mentioned are probably the last 2 you'll install, the ones in the battery compartment right behind the button to open mac.