Airsoft Jg M4 basic carbine not working correctly?

As i was firing fine in semi the trigger just stopped envoking any gearbox response and would just press in and do nothing for both semi and full auto modes. When i switched from semi to safe and then back again a few times their was some tightness when switching i didn't feel before and now even though the tightness stopped, i think the problem is related to that. What kind of problem does this sound like? What part is underneath the selector switch internally that could be partially obstructing switching firing modes? any responses for info would be appreciated, thank you