I have had this problem plenty of times. First thing you need to do is oil the gun. For simplistic sake, just by a bottle of the “special” marker oil from walmart. If you are ok with taking your marker apart, then take it apart and oil the hell out of both the bolt and seer, not to mention clean the innards while your at it. If that doesn’t fix it, then you might have “the cup seal of death” problem, which means a new part for the gun. but that is a last resort situation, if oiling the gun doesn’t solve the problem, try removing the spring and trigger, then shacking the gun back and forth, if the bolt gets stuck with out any gas or a spring, then there is something wrong with the bolt or sear, probably barbs from sheering.
If nothing here helps or you have more questions, feel free to ask me, I have worked and played as a pro ever since the Spider Compact 2000 was a brand new gun. I have experience with any and every kind of paintball gun you can imagine, including, but not limited to, the Tippmann Revolver and the Tippmann propane powered pump gun.