1- Sorry for the "site.ir" and not telling you assume it's my website. As in my country, mostly we refer something like test.ir or site.ir to assume this is you/my website, then we continue anything we want to tell or teach.
Firewall is disabled. I mean it was disabled when I opened Firewall Configuration! That surprised me!
2- I ran command
wget https://whmcs.communityand it downloaded index.html.
Because in Iran some websites are banned and not accessible via Iranian IP, I changed my IP to DE, but still it was unable to load.
I hit ctrl+u to see the source of the page, that it showed me complete source. But visually I see nothing.
3- As long as I remember, I've tried in Chrome and Firefox (Firefox's cache is always empty, it's set to be empty and cleared), but both showed the same that did not load.