After installing fresh magento on your server, if you are getting below message in your magento admin.
It means magento .htaccess are not working on your server.
So to solve this issue you have to change some lines inside apache config file.
simply go to /etc/apache2/sites-enabled/
here you will have to edit one file which name is like default.
Options Indexes FollowSymLinks MultiViews
allow from all
only change the AllowOverride value from None to All
Now you have to restart your apache webserver then it will work fine.
run this command to restart the server: service apache2 restart