Lightroom Classic will not load

What happens if you use Windows File Explorer, to navigate to your catalog, and double click on it?

Try resetting 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.

What has been changed on your system before the error occur?

Is your system up-to-date? Do you have installed all recent updates and patches for the operating system and the device drivers, especially the graphic driver. If you have a NVidia graphic card installed, make sure that you are using the recent Studio version of the driver, not the Game Ready version.

Which Lightroom version do you have installed.

Another reason can be a defective catalog. Hold the Ctrl-Key while starting LrC. This opens a catalog selection dialog. Then try to create a new one and see if this catalog works. If yes, you could then try to import your current catalog into the new one.

@Geoff McIlleron this is the Photoshop forum, try the Lightroom Classic forum instead