You did not mention if your revolver is Colt or Remington pattern, but the cure would be pretty much the same.
Remove the trigger guard and the combo spring for the trigger and bolt. When replacing this spring, be sure the long arm is facing toward the top of the gun and is positioned on the ledge on the trigger. That is what makes the trigger bear forward and engage the hammer notches. The short leg goes on the bolt to make it pop up and lock the cylinder. I hope this helps you.