We're sorry about the trouble experienced with Lightroom. We're here to help.
Where are the files located? Have you changed any settings recently? Did you try re-logging in?
I have got some steps for you to follow.
Quit Lightroom CC
Navigate to the catalog folder
In Mac Finder, go to Pictures. Right-click on Lightroom library.lrlibrary and choose "Show Package Contents."
In Windows Explorer, go to c:\users\<username>\AppData\Local\Adobe\Lightroom CC\Data
You'll see a folder with a long string of characters for the name. Open that.
Select any file that starts with "Managed Catalog" and delete or move the files to the desktop location in one single folder. Note: if you see an error trying to remove any of these files, reboot the computer, and then try to delete again. If any of these files are left behind, corruption will reoccur.
Start Lightroom CC. It will sync down your images from the cloud.
Let us know if the above steps help you fix this issue.