Could you please confirm which operating system are you using : windows or mac and its version?
Try to launch Lightroom with Control/command key and choose the option to create a new catalog.
If that works, go to File> Import from another catalog> choose the main catalog> import data from there.
My operating system is Windows 7.
Your advise did not help me.
What happened when you tried to create a new catalog?
Also, right click on Lightroom icon and choose run as administrator and let me know the result.
I can not create a new catalog at all.
And to run Lightroom as administrator help not, too.
Install the Microsoft C++ 2012 Re-distributable Update 4 from this link :
Download Visual C++ Redistributable for Visual Studio 2012 Update 4 from Official Microsoft Download Center
and then, launch Lightroom as administrator.
I did that already, too. No help.
Go to your backup catalogs
and open the most recent backed up catalog to check if you are able to open up that.
Remember to unzip the contents of the backup catalog first.