After upgrading, cannot login anymore

After upgrading the responsive theme directorypress to the latest version, at first all seemed ok –

Then suddenly I could not get back to admin, the admin pages all redirected to the domain itself (homepage)

After disabling the plugin 404 redirection, the site accepted to go to the admin section again, however I was logged out, so redirected to the login.php page, but this did not give me the login fields but came back with the search result page with the message “We have found 0 items matching your search.”

For example, if you click the link below it will show:
https://www.penisenlargementdrugs.org/wp-admin/

I have tried to fix it through
1. uploading the login.php again of the wp script
2. disabled all plugins > issue still exist
3. disabled the childtheme > issue still exist
4. disabled the DT folder > site goes blanco pages

I am now up to upload the old DT theme back and activate that through FTP (rename the latest DT version for now to DT-1 and upload the old DT theme as DT folder)

But that means I have to run the old version again and of course I want to have it updated with the new version.

Is it possible to fix this?

Thanks in advance

Ray