In case you don't know where the adjusting screw is, it is the screw between the two triggers.
If it is screwed in too far, it will prevent the front trigger from latching the rear, spring loaded trigger and holding it cocked.
A lot of people don't know exactly what that screw does and they often screw it in to adjust the trigger pull, thinking that doing this will make shooting the gun without the triggers being set will be easier.
Rather than making the unset front trigger easier to pull, it just makes the rear trigger impossible to set. Then, they think the trigger is broken and sell the gun.