Spring has come loose

Staples newly purchased will always be attached when purchased and that answers your question...wherever the device u are loading has a horizontal channel, there will be a loading window at the end. Take it apart by realeasing the cap or spring at the bottom and sliding the train of staples into the channel inside. Replace cap or spring lever to original position and secure. Stapler is now loaded.

Place the stapler horizontally in front of you, as though you were going to feed in paper from the right-hand side.
On the left of the stapler you will find the staple strip - the metalic box with two small holes in the top. Push the stable strip to the right and tilt upwards to release it. You should now be able to pull it out to the left.
Remove the staple strip completely, and place the new staples onto the track above the spring.
Re-attach the staple strip by reversing what you did to take it out. The end of the staple strip should sit across the track in the same way as the staples. Be aware that this time there will be more resistance as the staples push against the spring in the staple strip.

If the tool sounds like it is firing when its struck but its not driving staples, there may be a problem with the feed magazine. Possibly something stuck in the staple slot keeping them from sliding through. Or possible the pusher spring is weak. This spring feeds the staples into the unit.

There is a spring to push the staples into place. Bostitch was purchased by Dewalt and moved their parts lists to the web address below. Enter your model number and order the parts needed. Good luck with your future projects.
http://servicenet.bostitch.com/

At the back of the staple gun is a flat shaped metal piece. It's at the bottom. Push in, pull down, then pull the mechanism out. You'll see it's a metal rod with a spring, that is attached to that flat metal piece. The spring pushes against another flat metal piece, that has a hole in it, and travels back, and forth on the rod.

The flat metal piece that the spring pushes down the rod, pushes against the staples.

Remove this spring mechanism, slide the staples down the rails. The staples will be in the position of an upside down U. Replace the spring mechanism, and lock it back into place. (Push in, pull up)

Should, your question be in reference to the fact that you have staples loaded, but upon pressing the trigger nothing comes out:

In the front of the staple gun, is a flat metal piece that pushes down on the staples. One staple at a time. The flat metal piece is shoved down by spring pressure. The spring pressure is applied to the flat metal piece each time you squeeze the trigger. (Flat metal piece = Hammer)

Sometimes, Two staples try to come out. When they do, this flat metal hammer is stuck up in the gun. To free the flat metal hammer, remove the spring mechanism out of the back of the staple gun. (The spring mechanism discussed above) Remove any staples in the gun.
Try to use a flat blade screwdriver, and see if you can shove the flat metal hammer in the front of the gun -> UP.
(DO NOT have the staple gun pointing at your face! DO NOT squeeze the trigger! DO NOT use excessive force)

If this method is of no avail for you, you have to disassemble the gun, and remove the metal hammer, and stuck staple/s.

The Spring keep the Staples against the Stapler driving tool. Normally there is a metal pad to push against the staples, a rod that goes thru the Spring with a metal latch that locks inside the Stapler.

It sounds like a manufactor defect in wire harness or premature silinoid burn out,
or you simply need to make sure you plug into and outlet that works. Could be cheap but not worth repair,return as defect if possiable and buy new one before.

Please rate. Thanks jj505

The person that asked this is probably long gone, but in case anyone else comes across this... I had the exact same problem when I dropped this same stapler today and the spring came out. After examining it for a bit, I realized where the spring had to go and fixed it.
Open the stapler the same way you would as if you were replacing the staples and look at the top piece, towards the back. There will be an elongated black hook here to attach one end of the spring. The trick is where you route the spring after that... look towards the front end of the same top piece, and you'll see 2 holes in the metal. You need to push the spring up through the first hole, then pull it back down through the second hole (you may want to use a straightened paper clip to snag the spring so you can pull it through that second one), and only then do you attach the other end of the spring to the hook in the sliding metal piece that advances the staples in the staple holder.
And that's it!

pull out the spring at the end of the gun. turn the staple gun upside down. Lay the staples in the track pointed side up, push in the spring slide so that it locks. You are ready to staple.

I hae the same problem. I don't know the real names of the parts so I will make up my own and try to describe them. The problem with mine is that the "hammer" (the piece in front that slams down on the staple and shoots it out) is broken. The "hammer" has two notches that the tension spring (actually a metal bar with two tongs not to be confused with the spring the returns the handle to the at rest position) fits into. One of these notches on the hammer is broken. Therefore one side is not attached to the tension spring the causing the other side to slip off and since the hammer is not connect to the tension spring you get no resistance. Unfortunately I could not find anywhere that sells a replacement peice.