Rubenairsoft

Hello I bought an m1a1 thompson from snowwolf 3 years ago with a battery. After 2 years it kept jamming up. I went to an airsoft store to fix it. They said they changed the motor. I tested it and it didn't work. When I pull the trigger it clicks and doesn't shoot. My battery is an NiMH 8,4V 1100mah battery. I think it's because the battery isn't strong enough but I'm not sure. Can someone help me fix this problem please? With kind regards Ruben