So I saw a chipmunk the other day and didn't have time to grab my .22 talon ss so I grabbed the wife's .177 talon ss. I loaded it aimed and squeezed.  It went pffff and the pellet barely came out of the barrel.  I had just filled the tank a week or so ago. So I cocked it and when I returned the cocking lever to close position it must have made contact with the air tank top hat? Because it made a very small pfff sound.  Like a little air escaped? Anyone know what the problem could be? It has just been sitting in the gun rack no one messed with it that I know of.
   Thanks for the help.

The pressure in the tank helps keep the top hat valve closed.  The symptoms of the low powered "pfft" shot and the small leak when the breach is closed generally indicate low tank pressure.  

Did you check the pressure?  Although it was filled a week ago, a small leak may have occurred and it is leaking down over time.

Thanks for the reply. I will double check and or  refill it tonight