sounds to me that some nice person has wound the hammer spring adjuster in as far as possible in an effort to increase the guns power what i suggest is to prove the point is to remove the action from the stock take off the round end cap at the back of the gun release the allen key that holds the hammer spring adjuster and wind the thread out about three full turns then retry your cocking if it holds my guess is right and you will have to reset the hammer spring over a chrony to get the correct power always assuming it is non FAC if what i suspect is true the problem is that the hammer spring gets spring bound i.e. completly squased before the hammer is all the way back hence no cocking just a footnote if you find that you have cycled a pellet into the breach and the gun is not cocked simply remove the magazine before recocking thus not cyclig a second pellet and fire the gun in the normal way refit the magazine after emptying the gun hope this makes sense
engineer