First, be sure you are using the correct cleats, and that the cleats are going into the wood at the crease just above the tongue on the wood. If it's not, you may have to change shoes. If this still doesn't help, see page 6 of the manual, to change the nailer over to ratcheting. This allows for multiple strikes as needed to be sure the cleats set all the way. The plunger will now ratchet down and only return when it bottoms out. ****Please Note**** Ratcheting will only work if you make sure the nailer doesn't move at all between strikes. If it does, you may miss the cleat entirely on the second strike. Putting your foot on it is a common practice used by the pros.