I pull the trigger and get a rush of air but no nail shot. It has been working fine for the last several days. I've got it running on between 75 and 80 psi.

If the trigger is set to single fire, you will need to place the gun against the work then pull trigger as you have done. Try setting the trigger to bump fire and try again. If hear a thump inside the gun, remove the head and check that the head valve in not stuck from lack of lubrication. Easy test, remove the nails, remove trigger pin, remove trigger and manually push trigger firing valve. If the gun fires then suspect faulty trigger or safety arm not lifting enought to activate the trigger valve. Good luck

Best practice is to bump fire the gun to prevent double fire. Do not place the gun on the work and pull the trigger. This takes practice while using at an angle. Works better if the nose piece has rather sharp points to help nose to stay in postion while you bump. With trigger depressed, practice without nails bumping/hitting wood at different angles untill you can bump hit at the spot that you need the fastener. If the gun double fires while bump-firing, most likely all the safety/trip parts are worn/loose. Not expensive to replace. Good luck.

Dried up or broken O-ring.

A nail gun works on compressed air.
When you hook the air hose to the gun it fills a cylinder with air pressure.
When you pull the trigger. the cylinder pressure is released onto a firing pin that shoots the nail.
The air pressure line is also connected to the trigger and therefore the trigger has to be sealed.

When ever using a nail gun, you add a bit of gun oil in the back of the gun (not 3-in-1motor oil, it has to be non-detergent gun oil)

If you haven't used the gun in a while, it is best to oil up the gun and let the oil run down into the gun.
If you use anything but gun oil, the seals will give out.

Your trigger seal has given out. It is probably an 'O' ring. You can access it by taking it apart. Look for the O ring.
Bostich makes re-build kits for the different guns that you can buy on-line.
Back when I was in construction, there were several nail gun shops that sold and serviced nail guns, and sold nails to the contractors. I don't know if that business model is still active or if you have to send the guns to Bostich service center.

Bostitch nailers have two triggers available. Black trigger is rapid fire while the gray is single shot. Both triggers are usefull depending on type of work. Most people say that there is a degree of accuracy with single shot allowing for better placement of nail. If speed is your goal then use the black trigger to bump fire. More information and parts can be found at www.bostitch.com , look for "Support" tab, then "service / parts " find your model number from the pull-down list and search for the manual and parts list for needs. Good luck on your projects.

piston is probably jammed

This happens sometimes try holding it up against a board with the trigger depressed and then inset the battery.

The goal is to try to force the firing sequence to get the piston back to the right position with corded units this is simply done by attaching the air hose with the trigger pulled this causes air to rush into the gun chamber pushing the piston back and firing a nail out.

The cause of this is a misfire or jammed nail that stopped the piston in the wrong location so air will not build in the chamber correctly.

Hope that helps

I hope this doesn't offend you. What I'm suggesting is that you may not be using your nail gun correctly. Some people keep the trigger pulled and bounce the gun onto the wood. This technique works okay, but placement accuracy of the nail suffers. The other technique is to place the gun on the wood and pull the trigger USING TWO HANDS! This is the technique suggested by the manufacturer. The problem with this technique is that if you apply insufficient pressure to the gun (USING ONE HAND) the safety is not engage so you don't shoot a nail. What usually happens - I just witnessed this a couple of weeks ago - is that not enough pressure is applied while pulling the trigger so you push harder and end up bumping the gun which shoots a nail - because you have the trigger pulled, but the nail shot was a surprise so it causes another bump (and is more apt to bounce because you're using just one hand). Because it is a machine and can operate faster than your reflexes - it shoots another nail. This happens before you can lift it off of the wood, or remove your finger from the trigger. That's the reason I keep the trigger pulled and bounce it. I know that after the bounce I've set a nail, and can remove my finger from the trigger. When I need to accurately set a nail I always use two hands, press hard and pull the trigger, and release quickly. Only pull the trigger when you know you're about to set a nail, and are poised above the workpiece.

I found a broken retainer ring in the head of the nailer. It had the striker head jammed in the down position so when you pulled the trigger to arm the head with air pressure, the flooring nailer shot a nail.
Thanks .. 

Make sure you have at least 100 psi available and I would pretty much drown the sliders and other moving parts in something like Marvel Mystery Oil.

The problem that you describe is caused when the driver is not returning all the way back up to the top of the cylinder not allowing the nails to enter into position . You may have one of several problems including worn piston oring, bent driver, worn check valve, worn lower bumper, or low air pressure. Simple test is to manually push the driver blade back to top using a thin piece of metal that fits into bottom of gun. Be sure to disconnect from air supply when doing this. Good Luck