Try a different plug. Try a different computer. If it still doesn't work in BOTH cases, then swap the cable to the USB (working cable you know came from something working) on a different computer. If it still doesn't work then the 'USB' (don't know what you mean this is, as USB is the TYPE of connection NOT a device, so this can be a USB Radio, USB Drive, USB Printer, USB Mouse, etc.) is dead an you need to buy a new one.