When you say nothing happens do you mean the hammer strikes the valve and no air comes out?
Or some air comes out but not enough to reset the hammer?
When you dry fire it should move with enough force to move the gun. I'm guessing that it's sticking or slowing down between the reset and the valve.
Pull the bolt and hammer assembly out and check if there is any oring damage and/or crap around the hammer and lower tube.
Pull the valve and make sure the stem of the cup seal doesn't have nicks that could cause it to bind when struck.
Put your mask on and with the valve out and the back of the gun pointed at the wall, screw in your tank slowly to see if gas comes out. If it doesn't then there is something blocking the air hose or ASA.
Lube the stem, bolt and hammer orings and see if it feels stronger when dry firing.
Then gas up and try again.
If it still doesn't fire then your input pressure is way above the 800psi and you should try with a CO2 tank.