Categories not showing up in back end

I’ve logged in my WordPress back end as an admin and suddenly none of my categories are showing. It says I have 29 categories in the Dashboard, but when I click on Categories on the side panel it doesn’t show any of them. There are also no categories showing in the right side panel when I try to categorize a new post. I haven’t touched anything since my last login, and I have tried deactiving all plugins and still no luck. Any suggestions?