After looking at the instructions, and having had some click pen issues of my own, here is my experience (there are many others on here who have lots more experience than I).
The biggest pain with this type of click pen (for me) is to get the top barrel separated from the connector in the middle: I grasp both barrels and with some twisting and pulling accompanied bouts of frustration and not-for-children colorful adjectives have managed to disconnect them. After removing screwed on (chrome) clicker and the little spring,
The plastic mechanism needs to come out through the middle (the bottom of the top barrel. Since the plastic piece is tapered I can usually manage this by sticking the ink refill in and pulling(coaxing) it out. From there it's a matter of tapping out the clip-insert and the nib-insert (the HF punches or the right size bolt or whatever just fits in the tube).
As to why it wasn't clicking: make sure the white plastic mechanism is put together right...the inner piece needs to be free to move in the outer one so it will "plunge". The refill sometimes needs to be twisted just right so it's making the right contact with the plunger.
Hope this gives you some ideas...good luck.
