We are hosting our primary domain on HostGator, and we've recently created sub-domains on the primary domain with the following format: SubDomainName.PrimarySiteName.com
I can open the sub-domain files through the cPanel, and the folder that each sub-domain should take content from is correct. But when we try to open the sub-domains in the browser, we get the following error: "Server not found". It has been more than a month for now from the time we created the sub-domains. Also, sub-domains will sometimes open on one computer, but not another.
Using the CPanel for your account with Host Gator simply click on "Simple DNS Zone Editor" and then finally ADD an "A Name" for the sub domain. Your "A Name" would be your complete sub domain URL. Example: subdomain.yourmaindomain.com AND than add the IP address for your main domain.
I had this issue and was able to resolve it by simply adding the single A Name record.