Joomla 2.5.17 broken installation error jimport() not defined

[jlcbg]

I am trying to get this Joomla site admin back end up and running, the site itself works as should be but on trying to log into the administrator panel /administrator/index.php looks for a template in a folder that didn't exist when I started to look for the problem. I have created the folder and placed the standard login.php file in it.
On line 20 of the login.php file the is a jimport call jimport('joomla.filesystem.file'); which is the standard call at this point.
This is the error that is being thrown.
Fatal error: Call to undefined function jimport() in /home/mayvisio/public_html/administrator/templates/joomla_admin/login.php on line 20
login.php is being called via index.php in the administrator directory so I don't know why I am getting this error.
Can anybody shed some light on this?

[JTema]

Hello after a backup of your site files+db download a fresh joomla installation of 2.5.x version that your site have. Then unzip files and replace administrator folder with fresh joomla administrator folder.

[annahersh]

It may be best to download a 2.5 package and upload the entire admin template via file manager. Get it at https://downloads.joomla.org/cms/joomla25