I wouldnt buy a new AB or any parts just yet.
Do what Bob said but I would run a straight 10ft AirBrush line from the compressor with NO quick cupplings or anything directly to the AB. Then take the tip, cap, nozzle and needle out...push down on the trigger...If air comes out then the 3 holes in the cap are probably plugged.... if no air then I would guess there is valve issues
I had issues when trying to use quick cupplings. they diminish the flow and when your running 20-30lbs if you have a couple of them your done. It took me many of days to get my compressor and hoses set up and working right.