try creating a php info page.
Create a blank php page, name it phpinfo.php
add the following code:
<?php phpinfo(); ?>
and try to view that in the browser.
If you can only view that page by removing the .htaccess file, it sounds like there is a problem with the .htaccess file.
the only code in the htaccess file should be the one line:
AddType x-mapp-php5 .php
and it should be saved to the web root on your host server.