We're sorry about the trouble with Lightroom Classic. Would you mind sharing the exact version of Lightroom Classic you're using along with the version of Windows you're working on? Is you catalog saved on your computer's local storage or an external drive?
Try launching Lightroom Classic while pressing and holding the Alt key. When you do, you should get a window like I've shown in the screenshot.
Select your catalog and check the option to "test integrity of this catalog" and then click on Open. If Lightroom Classic finds an issue with the catalog, it will try to run a repair. If the catalog can be repaired, the app will do that and then open the catalog for you.