Problem with photos in the library

Are you using an iOS device? Did you recently update the app? If so you may have lost content that hadn't synced to the cloud. Please read this information from Adobe. https://helpx.adobe.com/lightroom-cc/kb/lightroom_mobile_5_4.html. If this is what happened to you, I am sorry. I wish I had a better answer for you.

Please elaborate on "I did a special settings for photos but I can't use it now."

As another mentioned, it would be beneficial to learn more about your system and application.

warmly/j

What version of Lightroom, and what OS? If you're using Lightroom on iOS, you need to see this thread from the Official Adobe feedback site: https://feedback.photoshop.com/photoshop_family/topics/lost-my-pictures-and-presets-after-update-today-18th-august-2020