intellij navigate to file stopped working

So we have a large project and I use the intellij navigate to file cntrl+shift+n all the time. I don't know what happened but now when I try and use it - it can't find anything. I haven't recently installed any plugins or anything. I've restarted intellij a couple times, checked the little filter icon to make sure I'm not filtering on anything...nothing seems to be working. Any ideas what I need to do to get it working again?