I think this is you problem:
Sorry for my English. The right arm of the spring is not correctly placed (black arrow). It must be on the left side of the piece where is resting now.
If this is your problem, and you want to solve it, I recommend you to follow this procedure:
Remove ONLY the upper screw. Then try to place the right arm of the spring in the correct place. How? I cannot see it!!. Just try it. You will know that it is correctly placed when you press the head of the piece (green arrow) and the piece returns to its original position (the spring is working). In my opinion, this is an easier option instead of removing all the parts.
This pictures are from a tutorial I wrote, but it is written in Spanish, here:
http://www.replic.as/viewtopic.php?t=7190&highlight=