Frog CMS

Just installed the Frog on my server, installation seems is ok.
But after the Frog is installed I can not load any pages including admin zone. Instead the loaded page the list of the files is shown (the files which are located in Frog’s subdirectory).
The only normally loaded page I can see is homepage when I type in my browser <frog’s_path>/index.php.
When I go to <frog’s_path>/admin/index.php the file list is shown again instead the admin zone.
What’s the problem? Is there a way to fix it?

My configuration:
PHP 5.2.9
SQL 5.0
Apache