Hello, Well to start off the SM-57 is a dynamic mic, meaning that it does not require phantom power to work. With that said, I would recommend opening up the mic by screwing off the bottom part to reveal where most of the electronics are. Check to see if there are any loose connections. If you don't find any put the mic back together, and try using it with a different XLR. I have found that XLRs often just stop working after a while if they are not wrapped properly, or not cared for.