Try launching directly from the catalog file. The default location for the LR folder is usually Pictures/My Pictures. Find your named catalog with the extension .lrcat
Double-click on the .lrcat file to launch.
If that doesn’t work you may need to replace the file with the .lrcat file from your last backup.
Is this a Windows 10 upgrade issue. If so try this,
Okay, I have tested this on two upgraded machines and it should work.
Right click your LR shortcut and click 'Troubleshoot Compatibility'
Click ' Troubleshoot Program'
Click 'Program worked with earlier versions of windows but won't run now'
Click 'Program requires additional permissions'
Click your previous windows version.
Click 'Test Program' If User Account Control is on you may need to click the shield icon on the task bar and give permission for changes and then click 'test program' again.
LR should open. Close LR
Click 'Save settings for this program'