(DP) air staple gun won't reload after shooting 1 staple

The most common cause of the gun not firing is loading it with the wrong staples. Look at the packaging for the staples and see if it lists the gun. Staples are NOT universal and are make for specific staple guns.

It "sounds like" it is jammed. You may have to pull out the staple with needle nosed pliers. e`1

How to Load Staple Gun

How to Troubleshoot Staple Gun Hunker

It won't HELP it, that's for sure. Go to a sporting goods store and purchase what's known as "Snap Caps" for your weapon's caliber. They're small plastic "ammo" that has a spring embedded where the primer/igniter would normally be located. When you dry-fire, the spring provides the proper resistance to the firing pin, preventing over-extension and premature wear/breakage of the pin. They're cheap, and since you have a wheel gun, you can load 'em once and shoot again and again and again. https://www.amazon.com/Tipton-Snap-Caps-Special-Magnum/dp/B0048KFHKQ/ref=sr_1_2?s=sporting-goods&ie=UTF8&qid=1491493949&sr=1-2&keywords=snap+caps+.38+special

Replace the O rings... sounds like its one in the firing valve ( rear cap of the gun behind the cylinder )

Check the instructions for cleaning and lubrication tips. Sounds like you have a buildup of the adhesive that holds staples in "sticks," and it's keeping the staple stick from moving forward into the firing position.

You shouldn't have to do anything to the MIIIFS flooring stapler to shoot 2" staples. It is designed to shoot 1 1/2" to 2" staples right out of the box. If your stapler won't feed 2" staples, check the magazine all the way up to the power head for any foreign material that may hold up your staples.

must dissemble the trigger mechanism and replace the broken or worn o ring that directs the air to the firing chamber.

sometimes mine won't shoot, and i find a single staple in the track, almost ready to fire out , but can't , they can be hard to see in the tract, i keep sharp pliers on hand to clear them. hope this helps

Make sure the staples you are using are compatable with your gun they should be type 53 or JT21 staples and they are not longer tham the gun is capable of taking I think the maximum capacity for this gun is 5/16 or 8mm.
Turn the gun upside down and pull back the carriage, the staples are laid in the empty chamber in the gun itself not on the carriage points facing in the direction they fire ie points facing you .
Push back the carriage this should slide over the strip of staples until the carriage clicks shut.
You should now be ready to fire, try and keep pressure down on the gun as the recoil can make the gun bounce and you will leave the staples proud.
Hope this helps.

I think you just answered your own question. I have had one single staple stuck at the "output" where the staple shoot out and it drove me insane for a few until I slowed my roll, took a deep breath and said, I have got to be smarter than a piece of metal here, and took a calm slow looksy. Sure enough, it was one loan staple causing a backup of the rest. I have also had issues with overloading staples which eventually makes the spring pushup rod become less forceful as it pushes the staples up for firing. Not an issue until you get towards the last dozen staples or so, which can also lead to the last staple not quite getting that millimeter push ahead, to shoot out correctly. These staple guns are like babies. Have to treat them nice and pamper them and heaven forbid you ever drop that stapler cause if dropped more than likely it will never quite be the same again. Telecom Tech 16 years.

its problem is too much oil or not enough. never the less, it needs taken apart and cleaned and inspected. make sure you are shooting the right guage and brand hardware. generic doesnt always work.