Huge gaps in clips and audio in Project, all Auto saves show same gaps

I opened my project, which I've been working on for weeks, and 70% of my clips and audio are gone. The sequence presents itself in the same way but with giant gaps where the clips, graphics, effects, and audio should be. All the autosave shows the same gaps. I've never experienced this before. Can anyone help? I can't find anything online that matches my description.