I need help with my airsoft gun?

have an hk g36c dual power airsoft gun(http://www.umarexusa.com/product/HK-G36C-AEG-Airsoft-Gun,194,66.htm). It doesn't work. I have a fully charged battery and I know that I didn't blow a fuse. When I have the gun on full auto, it makes a very faint sound when I hold the gun up to my ear. It sounds like a very small fire. I don't know what's wrong and I was wondering if it can be fixed. Please tell me anything that can help.