cant open LrC

[Enchanted_listener6244]

Can't open LR Classic. Get a message that the catalogue is open in another application. No idea what that is. Help please!

[GoldingD]

Did LrC not properly close last time you used it? Did it crash, or perhaps you forced quit LrC? 

Check for a lock file that did not get deleted.

• https://helpx.adobe.com/lightroom-classic/kb/lightroom-error-catalog-cannot-be-opened-lrcat-lock.htm...

[DdeGannes]

When LrC is open it creates a .lock (LOCK) file next to the Catalog file which has an extention .lrcat (LRCAT)  the lock file with the same name as the Catalog ending with the extention .lrcat.lock.

When you close the LrC application the LOCK file will be automatically deleted, however if the LrC application is closed unexpectedly e.g. loss of power the LOCK file will remain in place and prevent the Catalog from being opened and cause the error you are experiencing. 
Go to the folder which containes the Catalog file and if there is a LOCK file is present delete the file (do not delete the Catalog file ending ,lrcat).