lIGHTROOM CLASSIC

As @dj_paige wrote we need more informations about your issue and your system.

What you can try in a first step is to reset the preferences of Lightroom Classic:  How to reset Lightroom Classic preferences (adobe.com)

It's recommended to backup your preferences before you reset the preferences to the default settings: 

https://helpx.adobe.com/lightroom-classic/kb/preference-file-and-other-file-locations.html

Another possible issue can be a faulty catalog. Try to restore the catalog from the recent backup.

Disaster strikes - a corrupted catalog! | The Lightroom Queen

Lots and lots of details are needed. What version NUMBER of LrC do you have? What version NUMBER of Windows do you have? We need version NUMBERS and not words like latest or up-to-date.

What happens when you try to open LrC? Please describe in detail. If there is an error message, please tell us the exact unedited word-for-word error message.