Krak'it open and see if the nozzle's damaged or slipped off the tappet plate.
Ensure your hopup is completely off (the slider should be all the way forward) when testing. With it off...the barrel should not be obstructed by anything. If the hopup nub is pushing down into the barrel while the hopup is off (a little, little bit is ok...but not a lot) then you've got to look at the nub, rubber, hopup unit. The edges of the hopup rubber should be evenly seated and not buckled or twisted in any way.
With the hopup unit/barrel assembly out of the front end...drop a bb into it. It should sit on the edge of the hopup rubber. A slight push with something ( (an allen key works) should pop it past the lips of the hopup rubber and it should just roll down the barrel on it's own. Try a bunch of BBs....if they all go through...use those to test with. If they jam...toss the whole bunch of them.
When reassembling...make sure you don't have the wires jamming up the front of the mechbox and receiver/hopup. That will push the mechbox back and cause an air leak. The ring around the hopup unit should sit flush and tight up against the mechbox shell.
Best of luck,