Missing catalog data after upgrading PC

Hello,

I have a problem with a catalog. I build a new PC and changed everything except the hard drives.
When starting the new PC everything was fine but Lightroom was empty. So I searched for the catalog in the HD tried to start it but it said I have to update it to V12 which I did without concern.
The update didn't went through and I had to restart the System. After trying again a new catalog file was there it is 1,4 GB big and I thought nice the catalog should be back. But it was't it's just showing the list of the folders but not one picture. I tried the search bar and everything I could find to sync again but nothing worked.  I searched for other lrcat files found some but non of them included my pictures. I tried to start the old catalog file with an older version (V11) also didn't want to start without updating it.  I found some articles that said when you update your catalog it could be damaged and a lot of pictures could be missing. (https://helpx.adobe.com/lightroom-classic/kb/recover-catalog-images-resetting-lightroom.html)
I also called the support of Adobe but they couldn't help me either.  

So what can I do to get my catalog back to work again?

Thanks for helping.

Enclosed some screenshots of folders Lightroom etc.