3 out of 4 screws will not let you properly level the cooler and it will not operate properly.
Get all 4 screws started and loose.
Screw things down a little bit at a time in a crossing pattern.
if you cant get the 4th one in the you are not doing it right.
remove the cooler when you go to put it back on start in the top left only screw it in 1 turn the go to the bottom right 1 turn the top right only 1 turn the bottom left 1 turn do this in this pattern till all are tight
(Voice of experience here... we have had over a hundred computers fail in our company due to one of the 4 posts used in original intel heat sinks breaking off... thus only using 3 out of the 4 screws...)
3 out of 4 screws will not let you properly level the cooler and it will not operate properly.
Get all 4 screws started and loose.
Screw things down a little bit at a time in a crossing pattern.