Joomla how to remove the admin panel redirect to the main one?

Question

Joomla

We transferred the site archive to Joomla 3.2. Online store on JoomShopping (this is just for completeness). I deployed it on the server, everything works, but it does not let me into the admin panel. When you try to log in, /administrator immediately redirects to the main one, even the login form does not show.
What was done:
1. checked .htaccess
2. Re-uploaded the engine files, downloaded from the office. site
3. Deleted all plugins via ftp
4. I looked through the active template, I did not find signs of a php redirect
From the plugins - authentication and twofactorauth. There are no third-party to protect the admin panel
Where to dig further, tell me, please?

Answer 1

There were similar glitches when upgrading from 2.5.6 to 3. It was decided by disabling all plugins and reloading the distribution kit from the off site.