quoting the procedure:
"You start the pins fully extended! Not lowered. The misunderstanding is in this 'locking position'. This does not mean to lower the pins ahead of time. It refers to the BLACK PIN TOPS which screw either right or left. Look close, there is an arrow pictured on top of the black pin. First extend the pins (you may have to put the arrows in release position if they are currently locked, do this by turning with the arrow direction) then turn that pin all the way opposite to the direction indicated by the arrow, push them through and you're done".
a/c to my experience first disengage the HSF than pull all the pins up, align it on the mobo than push the opposite pins simultaneously until they snaps, don't be afraid of putting some pressure on it, after installing the HSF look at the back of the mobo u should be able to see the black ends of all 4 pins popping out from the white plastic fasteners, if it doesn't than try again.
Note that mobo should bent a little due to tension!
and yeah not to mention that u should do the above procedure with mobo out of the chassis!