We need more info.
Did the gun feed a shell into the chamber, and it failed to go off?
Was the primer struck, or struck lightly?
Did the gun fail to feed a shell out of the magazine at all and the chamber was empty?
If the gun fed a shell into the chamber and it simply failed to fire, the most likely suspect is a broken or damaged firing pin.
If the gun failed to feed a shell from the magazine and the chamber was empty, the most likely problem is that you failed to fully pull the forearm to the rear.
This is known as "short stroking" and is a common problem when people who haven't practiced enough with the gun simply fail to pull the forearm all the way back, especially when they try to operate the gun quickly.
I've seen people who refuse to believe this is happening until someone used a video camera to film them operating the gun.
The trick here is to practice operating the gun and make sure to pull the forearm smartly to the rear until it bumps to a positive stop before pushing it forward.
A possible problem is a weak magazine spring, or a dirty magazine tube.
In this case, the shells may not have enough spring pressure on them and when the gun is operated fast, the shells may not have enough spring pressure to force them out of the magazine and into the action before you push it closed.