Thanks for reaching out. I'll need more information to help you with this.
You can use the Creative Cloud app to check the version of Lightroom & do any pending updates. Has this happened since a recent change in your computer or a recent update in Lightroom? What troubleshooting steps have you tried?
If you have your files synced, please try out these steps.
Try opening Lightroom by right-clicking and selecting 'Run as Administrator as the first step.
If this does not help, try these steps:
Go to the following location
Press the Windows > Enter 'Run' > Type %localappdata%\Adobe
Rename the Lightroom CC folder as 'Lightroom CC.old' (add .old at the end)