Airsoft question, gun wont fire..?

My airsoft gun wont fire in semi or auto. I'm using .20g bb's... but the gun would dry fire a few times.. then i would have to remove the magazine so about 5 bb's could drop form the inside.. then i replaced it.. now it will not fire, it's a V4 CQB-R from torontoairsoft. PLease help btw the gun is still under warranty