Then you might want to debug the server process and post the output:
but my apache server is running. And all the sites are served. The System -.> system services list the web server as activated. Why would it report here as not running?
Check that the apache server listens to IP 127.0.0.1 too. Or your mysql permissions are wrong as I explained in the posts above so that the ispconfig server scrippt can not update the server status anymore.