I have a Bostitch BT1855. brand new. it only shoots air. please help.

https://toolsandmore.us/bostitch-180583-carrying-case.aspx
I think you have the BT1855 nailer. Here is the storage case. If this is not what you want, contact Bostitch.

of course there is

need new trigger assembly

Just air tool oil through the air inlet nipple

Have you serviced it recently? and is the gas in date? The pistons do dry out and have to be oiled with special oil.

Rather than try to repair it or look into it, call the dealer or take it back to him as you will invalidate your warranty if you do anything to the unit, and that is not worth it. Let the dealer worry about it.

Usually when you hear the pop of the compressed air and the driver does not move indicates that the driver blade is bent, broken, or stuck due to debris. Remove head and pull cylinder to examine. Parts are not expensice and are available as kit including driver and cylinder with related parts or just the driver. from WWW.bostitch.com or even ebay. If driver is bent, you can probably make adjustment and get more life. Good luck

Ensure that the gun is well lubricated to as per manual.

first make sure that you are using the right guage nails and if so I would return it to the place of purchase for replacement., the blowing of air could indicate a jammed nail in the track, look for that first and make sure the driver is retracting fully.

it sounds like the piston/driver might be stuck or the firing valve is malfunctioning. there are 4 screws to remove the top cap and you can see if the driver is damaged. Also before removing check to make sure there is not a nail jammed in the nose assembly. This tool is good for breaking the pin on the piston.