Stapler is jammed

Could be a broken or defective retaining latch

it is not a computer (off topic there) and is staple gun.
and is pure mechanical device.

yours is jammed or got wet and rusted out.

most guns like this (I have 2) just jam, very easy.
that is there character, to do that, ask any carpenter for help.
open it and using flashlight find the stables jammed inside, or worst case, IT IS EMPTY OF all stables.

To fix a staple jam in a stapler, you should first remove the jammed staples and check for any obstruction in the stapler that could be causing the jam. If the obstruction is still present, you will need to disassemble the stapler to remove it. Once the obstruction has been removed, you should check the stapler to make sure that all parts are in good condition and properly aligned. If necessary, you should replace any worn or broken parts. Additionally, you should ensure that you are using the correct staples for the stapler, as using the wrong staples can cause jams.

One of the screws - furthest away from where the staples exit - has a nut on it... Remove the nut, then - using pliers - back out the screw. When I did this, the spring returned, a bent staple fell out and once re-assembled I could use the stapler again (for a few turns). It seems like the stapler is VERY sensitive to bounce during the stapling, you must hold it very tight (and flat) to the material so that the staple doesn't jam inside the stapler. Lousy product.

there is no parts explosion that I have found for this tool on several different sites.

I searched for Powershot 5700M on Canon's website. There is no camera.

http://www.canon.com/

here is the link to manual:

http://servicenet.blackanddecker.com/Products/Detail/5700

good luck

Thanks

Here are the scanned images from the Black & Decker 5700 Powershot Instruction Manual. These are just the instructions and corresponding illustrations for how to load the stapler, but the full instruction manual is available here:
http://servicenet.blackanddecker.com/Products/Detail/5700#

Good luck!

Lovenheim posted this diagram on http://www.maybenow.com/ and maybe it'll help you...

An Arrow T-50, inexpensive and durable