for apache to handle php files, 3 lines are required:
This one in the main server configuration block, as the LoadModule
dorective only apply to server config context:
LoadModule php5_module /usr/lib/apache2-extramodules/libphp5.so
of cource type the right path to libphp5.so.
and these 2 line could be added to server configuration context or to a virtual host config context:
AddHandler php5-script .php
AddType text/html .php
make sure those apache directives applied to your apache configuration, no need for reinstalling I think, also your pleask will become non consistent when you do so.