Is it necessary to use filler on each crown staple in the underlay

Size Of Staple Used 1 1/4 in, 5/16 in length
1/4" Staple Gun Staples (SWI36114);
Swingline 101 Series 5/16" Staple Gun Staples (SWI36115)

If you google Heavy Duty Wide Crown 3/8 in Wire Staples there are hundred of sites that sell the staple amazon, Home depot, Lowes, Walmart

It's quite possibly under the cap it's the head valve. Does it shoot at all ?
If so hold the trigger after the shot listen for where air is leaking.

try a large pair of pliers.
straighten the staples as much as you can, grip one leg with the pliers about 1/8" from the wood, and tap the pliers with a mallet or wood block.
alternate "till you can grip the crown.

There are several brands of staples that will fit your stapler and the price will vary according to the depth of staple you are looking to buy. Arrow brand staples are the most common. All the ones I saw that fit the 9700 are Wide Crown Swingline Heavy Duty
Arrow 606 Wide Crown Swingline Heavy Duty 3 8 Inch Staples 1 000 Pack

Yes, underlayment provides protection against warping from moisture particularly if you are installing the floor over concrete. Moreover, underlayment eliminates the echo sounds that are generated from traffic on the floor.

I believe on that model you have to release the magazine latch, pull the lower half all the way back, load the staples into the upper half of the magazine, then close and latch the lower half. The staple pusher and spring are located in the lower half so the staples need to be in front of that for them to be properly pushed into the nose. Also make sure you are running the correct staple. There are 1/4" and 3/16" narrow crown staples out there and they don't interchange. The staples should slide freely in the magazine when they are loaded.

Galino.com should be able to get you a parts diagram and supply the part

Put the staples in the staple gun before you put in the tool.
http://www.arrowfastener.com/sites/default/files/T2025_manual.pdf

Do not be so afraid. Unscrew that big crown fully, pull off and then you will see the real setting crown(quite small one), called an underlayed crown.
That little chain is hard enough to withstand your pulls, unless you are drunk. :)))
When you get that small crown handy- you can set the time and all the features.
If the small crown is not moving, your watch is rusty and you will need a proper watchmakers help.
Don't forget to rate, please.