I need to know how to get my guitar to come through it. Everything lights up, but no sound. I used it at church a few times, so I know it works. It has a 4 channel select switch on both the reciever and the transmitter, but it also has an A and B swithches on back of the reciever and they have mute on top of them. I believe this could be the problem. Which way do I turn them. Please help