Instructions for both of my pneumatic nailers state that every so often put a few drops of nail gun lube oil in the fitting that the compressed air hose attaches to. I put two or three drops in every time I use it. A small bottle of oil came with the gun. I got a larger bottle at Lowe's.
I triggered a nail on my 18 ga brad nailer when there was already a nail stranded in the tip. I had to take the tip apart and extract the mess. One nail was welded to the channel and I had to twist it off with needle nosed pliers. This was due to improper air pressure setting on the tank; I was going back and forth between the 18 ga brad nailer and a 23 ga pin nailer, and forgot to change the pressure setting on the tank.
Your nailer might need a full rebuild, but I would first clear the nail jam in the tip, following instructions for this, and then put a good amount of oil in the air hole and then connect the air supply, let it sit for an hour and see if this will force oil into places it needs to be. If it is still unresponsive, let it sit with the pneumatic hose fitting up and see if the oil will drain down to where it the sticking is.
If this doesn't work, you could take the pressure cap off and put oil in there. Removing the pressure cap might be a challenge if you have never done it before. You might have to send the gun for professional repair.