This usually happens if there is a problem with the iPod / iPhone or Dock cable. Before replacing anything, you need to try the following:
- Make sure that it is has music on it
- Reboot the Apple device (if it is an iPhone, close all apps too before the reboot - a hard reset might work better)
- Update the iPod / IPhone if newer update version is available
- Check the charging status. If there is no charging then the problem is bigger, might be installation related
- Test the system with other Apple products too
- Disconnect and reconnect the Gateway hardware from the power
- Check the Dension website. There might be a specific update for the Gateway