Missing files questions are tough to answer because only you know what your typical workflow is, how and where you typically save and handle your audio files, and what you do with them. So it's a bit like you saying you've lost your wallet and asking for help locating it.
Still we can go through it together:
1. Did you get an alert when you opened that Logic project, stating that some of your audio files were missing?
2. How did you save this project prior to having this issue: as a package, as a folder? Onto your system drive, an external drive? Was the project moved, copied, backed up?
3. Where do the audio files come from: are they recordings from acoustic instruments? Bounced files from software synthesizers or samplers? Downloaded samples? Files provided by someone else via email, or some other way?
As for the issue of the track that shows a waveform but you can't hear it, could you post a screenshot of that with that track selected, the Inspector visible (so we can see the meters), during playback?