There are many reasons as to why a domain name may not be resolving to the server. Please find the possible reasons for the DNS resolving issues listed below:
Please check if your namservers have been properly configured or not. You need to set the nameservers as per the information provided in the hosting account welcome mail that was sent to you during the account registration.
Make sure that the domain is registered and not expired; this can be checked with a Whois lookup tool. You can use http://www.whoisresult.com to get the registration information.
Check if the A record is configured properly or not. Normally this setting is automatically configured by the Control panel. In case anyone has updated some manual entry in the A record of the website, then this section needs to be verified.
There is one more scenario i.e. if you are using different nameservers and don’t want to change the nameservers. In this case, your A records should be proper and need to point towards the A records of hosting provider.