Drupal not loading pages except homepage

Its due to clean URL. You have to enable mod_rewrite for rectifying this. If you are using Windows OS and want to enable mod_rewrite module then

1. find the httpd.conf file (usually you will find it in a folder called conf, config or something along those lines)
2. the httpd.conf file uncomment the line LoadModule rewrite_module modules/mod_rewrite.so (remove the pound '#' sign from in front of the line)
3. find the line ClearModuleList is uncommented then find and make sure that the line AddModule mod_rewrite.c is not commented out.