Need help with debugging Joomla site

Our joomla based website is working fine for the most part but there is a module that has stopped showing up. It was showing up earlier but now it is not. We don't know what changes we did that affected this module and we need a joomla expert to find what's wrong. This module does show up if we change the position to something else. But not at the position we want. Again, it was showing up at the required position earlier but not now.