Turn your velocity adjuster in--this makes the hammer hit the valve pin harder, causing more air to go through the bolt to the ball--and more air to push against the hammer. As Fubarius suggested, turn it to normal levels and try again.
Make sure your output pressure is high enough. Borrow someone's full CO2 tank and give it a try. Not sure why you're using HPA with such a cheap gun, but make sure your tank is a high-pressure output tank (800 psi or so).
If the problem is not solved, remove the bolt and hammer, clean out the insides of the inner and upper tubes (be sure not to leave any lint), replace the hammer o-ring (should be a standard bottle o-ring), lubricate, and reassemble.
If none of this works, you've basically gone through all the expected troubleshooting steps expected of a normal paintball player--you should call up Brass Eagle, and make them fix it--it's possible your valve spring is too strong, that the valve pin is too thick (not letting enough air through) or something like that.