yea, your http.conf and php.ini can be set up correctly and if the httpd and php binaries arent set up it wont run. once i updated the apache httpd to the latest version and lost php. all of my configuration files remained unchanged but the server didnt work. then i rebuilt it and it worked
when the installer sets up the os it'll configure apache php dependencies/additional modules (php, perl, mysql or postgresql, ldap...) and build the binary accordingly.
maybe you can try to rebuild php by its self
i have mine built with the following:
./configure i386-redhat-linux --prefix=/usr --exec-prefix=/usr --bindir=/usr/bin --sbindir=/usr/sbin --sysconfdir=/etc --datadir=/usr/share --includedir=/usr/include --libdir=/usr/lib --libexecdir=/usr/libexec --localstatedir=/var --sharedstatedir=/usr/com --mandir=/usr/share/man --infodir=/usr/share/info --prefix=/usr --with-config-file-path=/etc --enable-force-cgi-redirect --disable-debug --enable-pic --disable-rpath --enable-inline-optimization --with-bz2 --with-db3 --with-curl --with-dom=/usr --with-exec-dir=/usr/bin --with-freetype-dir=/usr --with-png-dir=/usr --with-gd --enable-gd-native-ttf --with-ttf --with-gdbm --with-gettext --with-ncurses --with-gmp --with-iconv --with-jpeg-dir=/usr --with-mm --with-openssl --with-png --with-pspell --with-regex=system --with-xml --with-expat-dir=/usr --with-zlib --with-layout=GNU --enable-bcmath --enable-debugger --enable-exif --enable-ftp --enable-magic-quotes --enable-safe-mode --enable-sockets --enable-sysvsem --enable-sysvshm --enable-discard-path --enable-track-vars --enable-trans-sid --enable-yp --enable-wddx --without-oci8 --with-imap=shared --with-imap-ssl --with-kerberos=/usr/kerberos --with-ldap=shared --with-mysql=shared,/usr --with-pgsql=shared --with-snmp=shared,/usr --with-snmp=shared --enable-ucd-snmp-hack --with-unixODBC=shared --enable-memory-limit --enable-bcmath --enable-shmop --enable-versioning --enable-calendar --enable-dbx --enable-dio --enable-mbstring --enable-mbstr-enc-trans --with-apxs=/usr/sbin/apxs