Login loop

I’m trying to log in but nothing happens. The same page appears again and again. Nothing has changed since last succesfull attempt. It’s not the server’s problem, neither my browser’s because i have a second site built with the same way in the same browser and it’s working fine. I tried with ftp to copy all root files, all wp-admin and wp-includes catalogs from a working backup but nothing!! I also reset the password in the database through phpadmin and i’m trying with an other username but still the same. I also deactivated all plugins. Please HELP!!! I want to see my admin environment.