Remove the magazine and shake out all excess water from the tool. WD-40 is merely for Water Displacement, hence the name WD-40. You need to lubricate with shop grade oil. Inspect the driver head to make sure the surface is flat and free of dings or nicks. In order for your tool to work properly it needs to be able to feed without interruption, and the driver head needs to be able to move back to **** and forward to fire without hinderance. After insuring that all parts are in proper working order, reassemble, load, and fire. This should fix your problem 90% of the time. If not, then check the magazine spring to make sure it is delivering a strong drive to the loaded staples or nails, if not, you need to either use more of either to put more pressure on the spring, or you need to replace the spring all together.