CO2 PROBLEM - AIRSOFT GUN?

I have just bought a Smith & Wesson M&P Airsoft gun, Black. I read the manual, and watched a couple reviews. I put the PellOil stuff on the top of the CO2 cartidge, and i loaded it in the gun. Then i put the mag filled with bbs, in the gun. I put the safety off, and fired. However when i shot the gun, nothing came out and there was no noise. Even now, when i just pull the trigger, there is no effect. Can someone please help? I have had this broken airsoft gun for about 2 weeks now, and i cannot find any solutions!