Can not login to administrator

when i go to my admin  /
/administrator  i get redirected to  index paage

any help to fix that.

Could be something wrong with mod_rewrite. Try /administrator/index.php
Also post the content of your .htaccess file.

thanks
I try /administrator/index.php and works

I also have a  oscommerce  as a subdirectory 
my-root/oscommerce
and when my clientents try to login theey get redirected to
/index   
this is causing a big pproblem

here is my    .httaccess


#
#  mod_rewrite in use
#

RewriteEngine On

#  Uncomment following line if you get 403 Forbidden Error

#Options +FollowSymLinks

#  Uncomment following line if your webserver's URL
#  is not directly related to physival file paths.
#  Update YourMamboDirectory (just / for root)

#RewriteBase /YourMamboDirectory

#
#  Rules
#

#RewriteCond %{REQUEST_URI} ^(/component/option,com) [NC,OR]
RewriteCond %{REQUEST_FILENAME} !\.(jpg|jpeg|gif|png|css|js|pl|txt)$
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule ^(.*) index.php

any help.....