Hamza,
Since you are running fastcgidispatch in standalone mode, let me assume you are using Apache 2.4 and you are looking at:
https://4js.com/online_documentation/fjs-gas-manual-html/?path=fjs-gas-manual#c_gas_config_mod_proxy_fcgi.htmlUsing the default conventions/names:
Make sure ps -aef | grep fastcgi shows you dispatcher running
http://host/gas/demos.html return the genero demo static html page ?
If not, your problem is indeed with Apache/fcgi or genero app server wrapper setup. You need to take a look at httpd.conf, apache error logs + wrapper.fcgi (as Guney suggested)
One common problem I have seen with this setup is permission on fcgi plugin
HTH
Laurent