Local Installation: install.php offered to download instead of running

Two things I would try:

1. Create a test.php file and only put <?php phpinfo(); ?> in it.

2. If that doesn’t work I would create an .htaccess file and put:

   AddType application/x-httpd-php .php .htm .html

   AddHandler x-httpd-php .php .htm .html

When you are asked to download a php file, it usually means that php isn’t working.