My Makita AT1150A stapler does not shoot any staples. Air comes out around the trigger when pressed but does not do anything else. What do I do to fix this problem?

Check to see if there is any foreign object jamming the striker bar. These units also have a diaphragm that sometimes needs to be replaced. If you do not have an automatic oiler on the line the diaphragm could have cracked allowing air to pass through. The Stapler can not build up the necessary pressure to fire the striker driving in the stapler. Damaged or cracked this will need to be replaced. Not difficult and easy to DIY job. Do NOT hook up to air when doing this service. Dirt and grim can also jam the unit. Clean lightly oil, work the unit and see if it frees up. I typically put a few drops of oil made for pneumatic tools directly into the unit. Each time I pull the pneumatic tools out to use. I do not have an inline oiler. :)
Typically at the Male nipple connection where the brass female connector hooks too. 2-3 drops only!
Hope this helps!