1st. Try a different magazine. It may be the magazine lip feeding incorrectly. Does it lock open afterwards? (is it GBB is it a NBB?)
2nd. Is the gun jamming? Maybe the magazine isn't completely inserted? It it the magazine that came with the gun?
Sounds like a feeding issue. Where is the gas coming out? Through the barrel or the ejection port?
Worst comes to worst, you educate yourself. See if there is a disassembly video on youtube and try to completely strip the gun. You'll see if there are any warped pins or torn O-rings. Be careful and take your time. It will take you a few hours but you'll learn a lot. Heck, I learned how to make my M9 go full auto because of youtube. lol. Do it at a workbench or kitchen table and use half of a cardboard box to put around the table ( so if any springs shoot out, they will hopefully bounce off the box.. but a good video will warn of this).http://www.airsplat.com/Items/AC-GAS-TOOL-KIT.htm