Note: The name of Apache 2 binary on Debian and SuSE OSes is "apache2," not "httpd" as it is on Red Hat-based Linux distributions or FreeBSD.
Make sure that "httpd" ("apache2" on SUsE and Debian) processes are shown in "ps" output:
# ps ax | grep httpd | grep -v grep
If not, try to start Apache from Plesk CP or via command line. If you get an error, check /var/log/httpd/error_log (/var/log/apache2/error_log on SuSE and Debian, /usr/local/psa/apache/logs/error_log on FreeBSD) for a detailed error description and read this article about Apache errors: 1488.
If no error appears, and Apache does not start silently, check that the /var/log/httpd/error_log (the path may differ for different operating systems) contains less than 2GB.
Make sure that Apache is listening on the both HTTP and HTTPS ports (80/443) on all needed IP addresses:
# netstat -l | grep http tcp 0 0 *:http *:* LISTEN tcp 0 0 *:https *:* LISTEN
# /usr/sbin/lsof -i | grep -i httpd httpd 22591 root 3u IPv6 2982023 TCP *:http (LISTEN) httpd 22591 root 4u IPv6 2982024 TCP *:https (LISTEN)
Note: "*:http" means that the HTTP port is listened to on all IP addresses. If you see "192.168.1.1:http" instead, it means that only connections to the "192.168.1.1" IP address are accepted by Apache.
To check that the Apache server is responsive, try to open a page from the server itself using "curl" or a console browser (e.g, Lynx, Links) .
# curl domain.tld