I have a 18 gauge 2" brad gun when you plug the

Check your compressor Pressure - it need to according to nail-gun specifications.
Usually it is mechanical pressure switch failure. Replace all with digital Controller.

The Bosch STN150-18 is a stapler. It will not shoot nails.

you should not have any problem with using any other brand of nail .18 gauge brad nail are pretty much the same in all brands.

Most nail guns are labeled with the longest nail/brad they can shoot but are capable of shooting shorter nails/brads. There should be a data sticker on the gun, usually on the magazine rail, or at least in the manual that tells you what pressure to operate the gun at, what guage brads the gun can shoot and the size of brads from shortest to longest it can handle.

look on the front of the tool.there is a dial right where the plastic meets the yellow housing.also look closely and you should see a diagram on the plastic telling you whitch way to go.

Shoots staples fine but brads jam or bend. Check that the part called "guide bar", #35 on the parts diagram isn't getting stuck in the channel of part #30.

The guide bar retracts into the channel when driving a staple and springs out of the channel to guide brads.

The guide bar can get stuck in the channel if it's bent or gummed up. (Bent is likely the result of driving a brad into an obstruction.)

The business end should look like this:

make sure you are using 18 gauge brads in the gun. also if the brads have gotten wet or are old, the paper or wax coating on the becomes weak and it will release more than one nail at a time. try different brads in it.

This is iffy... but PC nailers are nit picky. If you used someone elses nails, it can (and will) jam and mess up.
So, if Porter Cable nails are being used, clean and lube the nail shoot (with a few drops of air tool oil).

If that does not work, Invest 19 dollars in a new, 18 guage nailer at Harbor Freight. I have 2 of those and they have been trouble free for 3 years.

i would double check the plunger to make sure its resetting after each fire.

If the piston/driver is broken, the gun will fire however nailing will not take place because the piston will jam in the cylinder. Sometimes the cylinder will also crack when the driver goes. If the piston is not broken but stays down, then check the cylinder check valve, worn lower bumper, bent driver or cracked cylinder. 18 guage nailer has a very thin driver which will easily bend or break. Parts however are not expensive.